**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON https://guides.rubyonrails.org.** Rails Internationalization (I18n) API ===================================== The Ruby I18n (shorthand for _internationalization_) gem which is shipped with Ruby on Rails (starting from Rails 2.2) provides an easy-to-use and extensible framework for **translating your application to a single custom language** other than English or for **providing multi-language support** in your application. The process of "internationalization" usually means to abstract all strings and other locale specific bits (such as date or currency formats) out of your application. The process of "localization" means to provide translations and localized formats for these bits.[^1] So, in the process of _internationalizing_ your Rails application you have to: * Ensure you have support for i18n. * Tell Rails where to find locale dictionaries. * Tell Rails how to set, preserve, and switch locales. In the process of _localizing_ your application you'll probably want to do the following three things: * Replace or supplement Rails' default locale - e.g. date and time formats, month names, Active Record model names, etc. * Abstract strings in your application into keyed dictionaries - e.g. flash messages, static text in your views, etc. * Store the resulting dictionaries somewhere. This guide will walk you through the I18n API and contains a tutorial on how to internationalize a Rails application from the start. After reading this guide, you will know: * How I18n works in Ruby on Rails * How to correctly use I18n into a RESTful application in various ways * How to use I18n to translate Active Record errors or Action Mailer E-mail subjects * Some other tools to go further with the translation process of your application -------------------------------------------------------------------------------- NOTE: The Ruby I18n framework provides you with all necessary means for internationalization/localization of your Rails application. You may, also use various gems available to add additional functionality or features. See the [rails-i18n gem](https://github.com/svenfuchs/rails-i18n) for more information. How I18n in Ruby on Rails Works ------------------------------- Internationalization is a complex problem. Natural languages differ in so many ways (e.g. in pluralization rules) that it is hard to provide tools for solving all problems at once. For that reason the Rails I18n API focuses on: * providing support for English and similar languages out of the box * making it easy to customize and extend everything for other languages As part of this solution, **every static string in the Rails framework** - e.g. Active Record validation messages, time and date formats - **has been internationalized**. _Localization_ of a Rails application means defining translated values for these strings in desired languages. To localize store and update _content_ in your application (e.g. translate blog posts), see the [Translating model content](#translating-model-content) section. ### The Overall Architecture of the Library Thus, the Ruby I18n gem is split into two parts: * The public API of the i18n framework - a Ruby module with public methods that define how the library works * A default backend (which is intentionally named _Simple_ backend) that implements these methods As a user you should always only access the public methods on the I18n module, but it is useful to know about the capabilities of the backend. NOTE: It is possible to swap the shipped Simple backend with a more powerful one, which would store translation data in a relational database, GetText dictionary, or similar. See section [Using different backends](#using-different-backends) below. ### The Public I18n API The most important methods of the I18n API are: ```ruby translate # Lookup text translations localize # Localize Date and Time objects to local formats ``` These have the aliases #t and #l so you can use them like this: ```ruby I18n.t 'store.title' I18n.l Time.now ``` There are also attribute readers and writers for the following attributes: ```ruby load_path # Announce your custom translation files locale # Get and set the current locale default_locale # Get and set the default locale available_locales # Permitted locales available for the application enforce_available_locales # Enforce locale permission (true or false) exception_handler # Use a different exception_handler backend # Use a different backend ``` So, let's internationalize a simple Rails application from the ground up in the next chapters! Setup the Rails Application for Internationalization ---------------------------------------------------- There are a few steps to get up and running with I18n support for a Rails application. ### Configure the I18n Module Following the _convention over configuration_ philosophy, Rails I18n provides reasonable default translation strings. When different translation strings are needed, they can be overridden. Rails adds all `.rb` and `.yml` files from the `config/locales` directory to the **translations load path**, automatically. The default `en.yml` locale in this directory contains a sample pair of translation strings: ```yaml en: hello: "Hello world" ``` This means, that in the `:en` locale, the key _hello_ will map to the _Hello world_ string. Every string inside Rails is internationalized in this way, see for instance Active Model validation messages in the [`activemodel/lib/active_model/locale/en.yml`](https://github.com/rails/rails/blob/master/activemodel/lib/active_model/locale/en.yml) file or time and date formats in the [`activesupport/lib/active_support/locale/en.yml`](https://github.com/rails/rails/blob/master/activesupport/lib/active_support/locale/en.yml) file. You can use YAML or standard Ruby Hashes to store translations in the default (Simple) backend. The I18n library will use **English** as a **default locale**, i.e. if a different locale is not set, `:en` will be used for looking up translations. NOTE: The i18n library takes a **pragmatic approach** to locale keys (after [some discussion](https://groups.google.com/forum/#!topic/rails-i18n/FN7eLH2-lHA)), including only the _locale_ ("language") part, like `:en`, `:pl`, not the _region_ part, like `:"en-US"` or `:"en-GB"`, which are traditionally used for separating "languages" and "regional setting" or "dialects". Many international applications use only the "language" element of a locale such as `:cs`, `:th`, or `:es` (for Czech, Thai, and Spanish). However, there are also regional differences within different language groups that may be important. For instance, in the `:"en-US"` locale you would have $ as a currency symbol, while in `:"en-GB"`, you would have £. Nothing stops you from separating regional and other settings in this way: you just have to provide full "English - United Kingdom" locale in a `:"en-GB"` dictionary. The **translations load path** (`I18n.load_path`) is an array of paths to files that will be loaded automatically. Configuring this path allows for customization of translations directory structure and file naming scheme. NOTE: The backend lazy-loads these translations when a translation is looked up for the first time. This backend can be swapped with something else even after translations have already been announced. You can change the default locale as well as configure the translations load paths in `config/application.rb` as follows: ```ruby config.i18n.load_path += Dir[Rails.root.join('my', 'locales', '*.{rb,yml}')] config.i18n.default_locale = :de ``` The load path must be specified before any translations are looked up. To change the default locale from an initializer instead of `config/application.rb`: ```ruby # config/initializers/locale.rb # Where the I18n library should search for translation files I18n.load_path += Dir[Rails.root.join('lib', 'locale', '*.{rb,yml}')] # Permitted locales available for the application I18n.available_locales = [:en, :pt] # Set default locale to something other than :en I18n.default_locale = :pt ``` Note that appending directly to `I18n.load_path` instead of to the application's configured i18n will _not_ override translations from external gems. ### Managing the Locale across Requests A localized application will likely need to provide support for multiple locales. To accomplish this, the locale should be set at the beginning of each request so that all strings are translated using the desired locale during the lifetime of that request. The default locale is used for all translations unless `I18n.locale=` or `I18n.with_locale` is used. `I18n.locale` can leak into subsequent requests served by the same thread/process if it is not consistently set in every controller. For example executing `I18n.locale = :es` in one POST requests will have effects for all later requests to controllers that don't set the locale, but only in that particular thread/process. For that reason, instead of `I18n.locale =` you can use `I18n.with_locale` which does not have this leak issue. The locale can be set in an `around_action` in the `ApplicationController`: ```ruby around_action :switch_locale def switch_locale(&action) locale = params[:locale] || I18n.default_locale I18n.with_locale(locale, &action) end ``` This example illustrates this using a URL query parameter to set the locale (e.g. `http://example.com/books?locale=pt`). With this approach, `http://localhost:3000?locale=pt` renders the Portuguese localization, while `http://localhost:3000?locale=de` loads a German localization. The locale can be set using one of many different approaches. #### Setting the Locale from the Domain Name One option you have is to set the locale from the domain name where your application runs. For example, we want `www.example.com` to load the English (or default) locale, and `www.example.es` to load the Spanish locale. Thus the _top-level domain name_ is used for locale setting. This has several advantages: * The locale is an _obvious_ part of the URL. * People intuitively grasp in which language the content will be displayed. * It is very trivial to implement in Rails. * Search engines seem to like that content in different languages lives at different, inter-linked domains. You can implement it like this in your `ApplicationController`: ```ruby around_action :switch_locale def switch_locale(&action) locale = extract_locale_from_tld || I18n.default_locale I18n.with_locale(locale, &action) end # Get locale from top-level domain or return +nil+ if such locale is not available # You have to put something like: # 127.0.0.1 application.com # 127.0.0.1 application.it # 127.0.0.1 application.pl # in your /etc/hosts file to try this out locally def extract_locale_from_tld parsed_locale = request.host.split('.').last I18n.available_locales.map(&:to_s).include?(parsed_locale) ? parsed_locale : nil end ``` We can also set the locale from the _subdomain_ in a very similar way: ```ruby # Get locale code from request subdomain (like http://it.application.local:3000) # You have to put something like: # 127.0.0.1 gr.application.local # in your /etc/hosts file to try this out locally def extract_locale_from_subdomain parsed_locale = request.subdomains.first I18n.available_locales.map(&:to_s).include?(parsed_locale) ? parsed_locale : nil end ``` If your application includes a locale switching menu, you would then have something like this in it: ```ruby link_to("Deutsch", "#{APP_CONFIG[:deutsch_website_url]}#{request.env['PATH_INFO']}") ``` assuming you would set `APP_CONFIG[:deutsch_website_url]` to some value like `http://www.application.de`. This solution has aforementioned advantages, however, you may not be able or may not want to provide different localizations ("language versions") on different domains. The most obvious solution would be to include locale code in the URL params (or request path). #### Setting the Locale from URL Params The most usual way of setting (and passing) the locale would be to include it in URL params, as we did in the `I18n.with_locale(params[:locale], &action)` _around_action_ in the first example. We would like to have URLs like `www.example.com/books?locale=ja` or `www.example.com/ja/books` in this case. This approach has almost the same set of advantages as setting the locale from the domain name: namely that it's RESTful and in accord with the rest of the World Wide Web. It does require a little bit more work to implement, though. Getting the locale from `params` and setting it accordingly is not hard; including it in every URL and thus **passing it through the requests** is. To include an explicit option in every URL, e.g. `link_to(books_url(locale: I18n.locale))`, would be tedious and probably impossible, of course. Rails contains infrastructure for "centralizing dynamic decisions about the URLs" in its [`ApplicationController#default_url_options`](https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Base.html#method-i-default_url_options), which is useful precisely in this scenario: it enables us to set "defaults" for [`url_for`](https://api.rubyonrails.org/classes/ActionDispatch/Routing/UrlFor.html#method-i-url_for) and helper methods dependent on it (by implementing/overriding `default_url_options`). We can include something like this in our `ApplicationController` then: ```ruby # app/controllers/application_controller.rb def default_url_options { locale: I18n.locale } end ``` Every helper method dependent on `url_for` (e.g. helpers for named routes like `root_path` or `root_url`, resource routes like `books_path` or `books_url`, etc.) will now **automatically include the locale in the query string**, like this: `http://localhost:3001/?locale=ja`. You may be satisfied with this. It does impact the readability of URLs, though, when the locale "hangs" at the end of every URL in your application. Moreover, from the architectural standpoint, locale is usually hierarchically above the other parts of the application domain: and URLs should reflect this. You probably want URLs to look like this: `http://www.example.com/en/books` (which loads the English locale) and `http://www.example.com/nl/books` (which loads the Dutch locale). This is achievable with the "over-riding `default_url_options`" strategy from above: you just have to set up your routes with [`scope`](https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Scoping.html): ```ruby # config/routes.rb scope "/:locale" do resources :books end ``` Now, when you call the `books_path` method you should get `"/en/books"` (for the default locale). A URL like `http://localhost:3001/nl/books` should load the Dutch locale, then, and following calls to `books_path` should return `"/nl/books"` (because the locale changed). WARNING. Since the return value of `default_url_options` is cached per request, the URLs in a locale selector cannot be generated invoking helpers in a loop that sets the corresponding `I18n.locale` in each iteration. Instead, leave `I18n.locale` untouched, and pass an explicit `:locale` option to the helper, or edit `request.original_fullpath`. If you don't want to force the use of a locale in your routes you can use an optional path scope (denoted by the parentheses) like so: ```ruby # config/routes.rb scope "(:locale)", locale: /en|nl/ do resources :books end ``` With this approach you will not get a `Routing Error` when accessing your resources such as `http://localhost:3001/books` without a locale. This is useful for when you want to use the default locale when one is not specified. Of course, you need to take special care of the root URL (usually "homepage" or "dashboard") of your application. A URL like `http://localhost:3001/nl` will not work automatically, because the `root to: "dashboard#index"` declaration in your `routes.rb` doesn't take locale into account. (And rightly so: there's only one "root" URL.) You would probably need to map URLs like these: ```ruby # config/routes.rb get '/:locale' => 'dashboard#index' ``` Do take special care about the **order of your routes**, so this route declaration does not "eat" other ones. (You may want to add it directly before the `root :to` declaration.) NOTE: Have a look at various gems which simplify working with routes: [routing_filter](https://github.com/svenfuchs/routing-filter/tree/master), [rails-translate-routes](https://github.com/francesc/rails-translate-routes), [route_translator](https://github.com/enriclluelles/route_translator). #### Setting the Locale from User Preferences An application with authenticated users may allow users to set a locale preference through the application's interface. With this approach, a user's selected locale preference is persisted in the database and used to set the locale for authenticated requests by that user. ```ruby around_action :switch_locale def switch_locale(&action) locale = current_user.try(:locale) || I18n.default_locale I18n.with_locale(locale, &action) end ``` #### Choosing an Implied Locale When an explicit locale has not been set for a request (e.g. via one of the above methods), an application should attempt to infer the desired locale. ##### Inferring Locale from the Language Header The `Accept-Language` HTTP header indicates the preferred language for request's response. Browsers [set this header value based on the user's language preference settings](http://www.w3.org/International/questions/qa-lang-priorities), making it a good first choice when inferring a locale. A trivial implementation of using an `Accept-Language` header would be: ```ruby def switch_locale(&action) logger.debug "* Accept-Language: #{request.env['HTTP_ACCEPT_LANGUAGE']}" locale = extract_locale_from_accept_language_header logger.debug "* Locale set to '#{locale}'" I18n.with_locale(locale, &action) end private def extract_locale_from_accept_language_header request.env['HTTP_ACCEPT_LANGUAGE'].scan(/^[a-z]{2}/).first end ``` In practice, more robust code is necessary to do this reliably. Iain Hecker's [http_accept_language](https://github.com/iain/http_accept_language/tree/master) library or Ryan Tomayko's [locale](https://github.com/rack/rack-contrib/blob/master/lib/rack/contrib/locale.rb) Rack middleware provide solutions to this problem. ##### Inferring the Locale from IP Geolocation The IP address of the client making the request can be used to infer the client's region and thus their locale. Services such as [GeoIP Lite Country](http://www.maxmind.com/app/geolitecountry) or gems like [geocoder](https://github.com/alexreisner/geocoder) can be used to implement this approach. In general, this approach is far less reliable than using the language header and is not recommended for most web applications. #### Storing the Locale from the Session or Cookies WARNING: You may be tempted to store the chosen locale in a _session_ or a *cookie*. However, **do not do this**. The locale should be transparent and a part of the URL. This way you won't break people's basic assumptions about the web itself: if you send a URL to a friend, they should see the same page and content as you. A fancy word for this would be that you're being [*RESTful*](https://en.wikipedia.org/wiki/Representational_State_Transfer). Read more about the RESTful approach in [Stefan Tilkov's articles](https://www.infoq.com/articles/rest-introduction). Sometimes there are exceptions to this rule and those are discussed below. Internationalization and Localization ------------------------------------- OK! Now you've initialized I18n support for your Ruby on Rails application and told it which locale to use and how to preserve it between requests. Next we need to _internationalize_ our application by abstracting every locale-specific element. Finally, we need to _localize_ it by providing necessary translations for these abstracts. Given the following example: ```ruby # config/routes.rb Rails.application.routes.draw do root to: "home#index" end ``` ```ruby # app/controllers/application_controller.rb class ApplicationController < ActionController::Base around_action :switch_locale def switch_locale(&action) locale = params[:locale] || I18n.default_locale I18n.with_locale(locale, &action) end end ``` ```ruby # app/controllers/home_controller.rb class HomeController < ApplicationController def index flash[:notice] = "Hello Flash" end end ``` ```html+erb # app/views/home/index.html.erb
<%= flash[:notice] %>
``` ![rails i18n demo untranslated](images/i18n/demo_untranslated.png) ### Abstracting Localized Code There are two strings in our code that are in English and that users will be rendered in our response ("Hello Flash" and "Hello World"). In order to internationalize this code, these strings need to be replaced by calls to Rails' `#t` helper with an appropriate key for each string: ```ruby # app/controllers/home_controller.rb class HomeController < ApplicationController def index flash[:notice] = t(:hello_flash) end end ``` ```html+erb # app/views/home/index.html.erb<%= flash[:notice] %>
``` Now, when this view is rendered, it will show an error message which tells you that the translations for the keys `:hello_world` and `:hello_flash` are missing. ![rails i18n demo translation missing](images/i18n/demo_translation_missing.png) NOTE: Rails adds a `t` (`translate`) helper method to your views so that you do not need to spell out `I18n.t` all the time. Additionally this helper will catch missing translations and wrap the resulting error message into a ``. ### Providing Translations for Internationalized Strings Add the missing translations into the translation dictionary files: ```yaml # config/locales/en.yml en: hello_world: Hello world! hello_flash: Hello flash! ``` ```yaml # config/locales/pirate.yml pirate: hello_world: Ahoy World hello_flash: Ahoy Flash ``` Because the `default_locale` hasn't changed, translations use the `:en` locale and the response renders the english strings: ![rails i18n demo translated to English](images/i18n/demo_translated_en.png) If the locale is set via the URL to the pirate locale (`http://localhost:3000?locale=pirate`), the response renders the pirate strings: ![rails i18n demo translated to pirate](images/i18n/demo_translated_pirate.png) NOTE: You need to restart the server when you add new locale files. You may use YAML (`.yml`) or plain Ruby (`.rb`) files for storing your translations in SimpleStore. YAML is the preferred option among Rails developers. However, it has one big disadvantage. YAML is very sensitive to whitespace and special characters, so the application may not load your dictionary properly. Ruby files will crash your application on first request, so you may easily find what's wrong. (If you encounter any "weird issues" with YAML dictionaries, try putting the relevant portion of your dictionary into a Ruby file.) If your translations are stored in YAML files, certain keys must be escaped. They are: * true, on, yes * false, off, no Examples: ```yaml # config/locales/en.yml en: success: 'true': 'True!' 'on': 'On!' 'false': 'False!' failure: true: 'True!' off: 'Off!' false: 'False!' ``` ```ruby I18n.t 'success.true' # => 'True!' I18n.t 'success.on' # => 'On!' I18n.t 'success.false' # => 'False!' I18n.t 'failure.false' # => Translation Missing I18n.t 'failure.off' # => Translation Missing I18n.t 'failure.true' # => Translation Missing ``` ### Passing Variables to Translations One key consideration for successfully internationalizing an application is to avoid making incorrect assumptions about grammar rules when abstracting localized code. Grammar rules that seem fundamental in one locale may not hold true in another one. Improper abstraction is shown in the following example, where assumptions are made about the ordering of the different parts of the translation. Note that Rails provides a `number_to_currency` helper to handle the following case. ```erb # app/views/products/show.html.erb <%= "#{t('currency')}#{@product.price}" %> ``` ```yaml # config/locales/en.yml en: currency: "$" ``` ```yaml # config/locales/es.yml es: currency: "€" ``` If the product's price is 10 then the proper translation for Spanish is "10 €" instead of "€10" but the abstraction cannot give it. To create proper abstraction, the I18n gem ships with a feature called variable interpolation that allows you to use variables in translation definitions and pass the values for these variables to the translation method. Proper abstraction is shown in the following example: ```erb # app/views/products/show.html.erb <%= t('product_price', price: @product.price) %> ``` ```yaml # config/locales/en.yml en: product_price: "$%{price}" ``` ```yaml # config/locales/es.yml es: product_price: "%{price} €" ``` All grammatical and punctuation decisions are made in the definition itself, so the abstraction can give a proper translation. NOTE: The `default` and `scope` keywords are reserved and can't be used as variable names. If used, an `I18n::ReservedInterpolationKey` exception is raised. If a translation expects an interpolation variable, but this has not been passed to `#translate`, an `I18n::MissingInterpolationArgument` exception is raised. ### Adding Date/Time Formats OK! Now let's add a timestamp to the view, so we can demo the **date/time localization** feature as well. To localize the time format you pass the Time object to `I18n.l` or (preferably) use Rails' `#l` helper. You can pick a format by passing the `:format` option - by default the `:default` format is used. ```erb # app/views/home/index.html.erb<%= flash[:notice] %>
<%= l Time.now, format: :short %>
``` And in our pirate translations file let's add a time format (it's already there in Rails' defaults for English): ```yaml # config/locales/pirate.yml pirate: time: formats: short: "arrrround %H'ish" ``` So that would give you: ![rails i18n demo localized time to pirate](images/i18n/demo_localized_pirate.png) TIP: Right now you might need to add some more date/time formats in order to make the I18n backend work as expected (at least for the 'pirate' locale). Of course, there's a great chance that somebody already did all the work by **translating Rails' defaults for your locale**. See the [rails-i18n repository at GitHub](https://github.com/svenfuchs/rails-i18n/tree/master/rails/locale) for an archive of various locale files. When you put such file(s) in `config/locales/` directory, they will automatically be ready for use. ### Inflection Rules for Other Locales Rails allows you to define inflection rules (such as rules for singularization and pluralization) for locales other than English. In `config/initializers/inflections.rb`, you can define these rules for multiple locales. The initializer contains a default example for specifying additional rules for English; follow that format for other locales as you see fit. ### Localized Views Let's say you have a _BooksController_ in your application. Your _index_ action renders content in `app/views/books/index.html.erb` template. When you put a _localized variant_ of this template: `index.es.html.erb` in the same directory, Rails will render content in this template, when the locale is set to `:es`. When the locale is set to the default locale, the generic `index.html.erb` view will be used. (Future Rails versions may well bring this _automagic_ localization to assets in `public`, etc.) You can make use of this feature, e.g. when working with a large amount of static content, which would be clumsy to put inside YAML or Ruby dictionaries. Bear in mind, though, that any change you would like to do later to the template must be propagated to all of them. ### Organization of Locale Files When you are using the default SimpleStore shipped with the i18n library, dictionaries are stored in plain-text files on the disk. Putting translations for all parts of your application in one file per locale could be hard to manage. You can store these files in a hierarchy which makes sense to you. For example, your `config/locales` directory could look like this: ``` |-defaults |---es.yml |---en.yml |-models |---book |-----es.yml |-----en.yml |-views |---defaults |-----es.yml |-----en.yml |---books |-----es.yml |-----en.yml |---users |-----es.yml |-----en.yml |---navigation |-----es.yml |-----en.yml ``` This way, you can separate model and model attribute names from text inside views, and all of this from the "defaults" (e.g. date and time formats). Other stores for the i18n library could provide different means of such separation. NOTE: The default locale loading mechanism in Rails does not load locale files in nested dictionaries, like we have here. So, for this to work, we must explicitly tell Rails to look further: ```ruby # config/application.rb config.i18n.load_path += Dir[Rails.root.join('config', 'locales', '**', '*.{rb,yml}')] ``` Overview of the I18n API Features --------------------------------- You should have a good understanding of using the i18n library now and know how to internationalize a basic Rails application. In the following chapters, we'll cover its features in more depth. These chapters will show examples using both the `I18n.translate` method as well as the [`translate` view helper method](https://api.rubyonrails.org/classes/ActionView/Helpers/TranslationHelper.html#method-i-translate) (noting the additional feature provide by the view helper method). Covered are features like these: * looking up translations * interpolating data into translations * pluralizing translations * using safe HTML translations (view helper method only) * localizing dates, numbers, currency, etc. ### Looking up Translations #### Basic Lookup, Scopes, and Nested Keys Translations are looked up by keys which can be both Symbols or Strings, so these calls are equivalent: ```ruby I18n.t :message I18n.t 'message' ``` The `translate` method also takes a `:scope` option which can contain one or more additional keys that will be used to specify a "namespace" or scope for a translation key: ```ruby I18n.t :record_invalid, scope: [:activerecord, :errors, :messages] ``` This looks up the `:record_invalid` message in the Active Record error messages. Additionally, both the key and scopes can be specified as dot-separated keys as in: ```ruby I18n.translate "activerecord.errors.messages.record_invalid" ``` Thus the following calls are equivalent: ```ruby I18n.t 'activerecord.errors.messages.record_invalid' I18n.t 'errors.messages.record_invalid', scope: :activerecord I18n.t :record_invalid, scope: 'activerecord.errors.messages' I18n.t :record_invalid, scope: [:activerecord, :errors, :messages] ``` #### Defaults When a `:default` option is given, its value will be returned if the translation is missing: ```ruby I18n.t :missing, default: 'Not here' # => 'Not here' ``` If the `:default` value is a Symbol, it will be used as a key and translated. One can provide multiple values as default. The first one that results in a value will be returned. E.g., the following first tries to translate the key `:missing` and then the key `:also_missing.` As both do not yield a result, the string "Not here" will be returned: ```ruby I18n.t :missing, default: [:also_missing, 'Not here'] # => 'Not here' ``` #### Bulk and Namespace Lookup To look up multiple translations at once, an array of keys can be passed: ```ruby I18n.t [:odd, :even], scope: 'errors.messages' # => ["must be odd", "must be even"] ``` Also, a key can translate to a (potentially nested) hash of grouped translations. E.g., one can receive _all_ Active Record error messages as a Hash with: ```ruby I18n.t 'activerecord.errors.messages' # => {:inclusion=>"is not included in the list", :exclusion=> ... } ``` If you want to perform interpolation on a bulk hash of translations, you need to pass `deep_interpolation: true` as a parameter. When you have the following dictionary: ```yaml en: welcome: title: "Welcome!" content: "Welcome to the %{app_name}" ``` then the nested interpolation will be ignored without the setting: ```ruby I18n.t 'welcome', app_name: 'book store' # => {:title=>"Welcome!", :content=>"Welcome to the %{app_name}"} I18n.t 'welcome', deep_interpolation: true, app_name: 'book store' # => {:title=>"Welcome!", :content=>"Welcome to the book store"} ``` #### "Lazy" Lookup Rails implements a convenient way to look up the locale inside _views_. When you have the following dictionary: ```yaml es: books: index: title: "Título" ``` you can look up the `books.index.title` value **inside** `app/views/books/index.html.erb` template like this (note the dot): ```erb <%= t '.title' %> ``` NOTE: Automatic translation scoping by partial is only available from the `translate` view helper method. "Lazy" lookup can also be used in controllers: ```yaml en: books: create: success: Book created! ``` This is useful for setting flash messages for instance: ```ruby class BooksController < ApplicationController def create # ... redirect_to books_url, notice: t('.success') end end ``` ### Pluralization In many languages — including English — there are only two forms, a singular and a plural, for a given string, e.g. "1 message" and "2 messages". Other languages ([Arabic](http://www.unicode.org/cldr/charts/latest/supplemental/language_plural_rules.html#ar), [Japanese](http://www.unicode.org/cldr/charts/latest/supplemental/language_plural_rules.html#ja), [Russian](http://www.unicode.org/cldr/charts/latest/supplemental/language_plural_rules.html#ru) and many more) have different grammars that have additional or fewer [plural forms](http://cldr.unicode.org/index/cldr-spec/plural-rules). Thus, the I18n API provides a flexible pluralization feature. The `:count` interpolation variable has a special role in that it both is interpolated to the translation and used to pick a pluralization from the translations according to the pluralization rules defined in the pluralization backend. By default, only the English pluralization rules are applied. ```ruby I18n.backend.store_translations :en, inbox: { zero: 'no messages', # optional one: 'one message', other: '%{count} messages' } I18n.translate :inbox, count: 2 # => '2 messages' I18n.translate :inbox, count: 1 # => 'one message' I18n.translate :inbox, count: 0 # => 'no messages' ``` The algorithm for pluralizations in `:en` is as simple as: ```ruby lookup_key = :zero if count == 0 && entry.has_key?(:zero) lookup_key ||= count == 1 ? :one : :other entry[lookup_key] ``` The translation denoted as `:one` is regarded as singular, and the `:other` is used as plural. If the count is zero, and a `:zero` entry is present, then it will be used instead of `:other`. If the lookup for the key does not return a Hash suitable for pluralization, an `I18n::InvalidPluralizationData` exception is raised. #### Locale-specific rules The I18n gem provides a Pluralization backend that can be used to enable locale-specific rules. Include it to the Simple backend, then add the localized pluralization algorithms to translation store, as `i18n.plural.rule`. ```ruby I18n::Backend::Simple.include(I18n::Backend::Pluralization) I18n.backend.store_translations :pt, i18n: { plural: { rule: lambda { |n| [0, 1].include?(n) ? :one : :other } } } I18n.backend.store_translations :pt, apples: { one: 'one or none', other: 'more than one' } I18n.t :apples, count: 0, locale: :pt # => 'one or none' ``` Alternatively, the separate gem [rails-i18n](https://github.com/svenfuchs/rails-i18n) can be used to provide a fuller set of locale-specific pluralization rules. ### Setting and Passing a Locale The locale can be either set pseudo-globally to `I18n.locale` (which uses `Thread.current` like, e.g., `Time.zone`) or can be passed as an option to `#translate` and `#localize`. If no locale is passed, `I18n.locale` is used: ```ruby I18n.locale = :de I18n.t :foo I18n.l Time.now ``` Explicitly passing a locale: ```ruby I18n.t :foo, locale: :de I18n.l Time.now, locale: :de ``` The `I18n.locale` defaults to `I18n.default_locale` which defaults to :`en`. The default locale can be set like this: ```ruby I18n.default_locale = :de ``` ### Using Safe HTML Translations Keys with a '_html' suffix and keys named 'html' are marked as HTML safe. When you use them in views the HTML will not be escaped. ```yaml # config/locales/en.yml en: welcome: welcome! hello_html: hello! title: html: title! ``` ```html+erb # app/views/home/index.html.erb