diff --git a/app/assets/stylesheets/pages/projects.scss b/app/assets/stylesheets/pages/projects.scss
index aa83e5bdebc..2a41a045e71 100644
--- a/app/assets/stylesheets/pages/projects.scss
+++ b/app/assets/stylesheets/pages/projects.scss
@@ -754,6 +754,11 @@
   }
 }
 
+.repository-languages-bar {
+  height: 6px;
+  margin-bottom: 8px;
+}
+
 pre.light-well {
   border-color: $well-light-border;
 }
diff --git a/app/helpers/repository_languages_helper.rb b/app/helpers/repository_languages_helper.rb
new file mode 100644
index 00000000000..9a842cf5ce0
--- /dev/null
+++ b/app/helpers/repository_languages_helper.rb
@@ -0,0 +1,16 @@
+module RepositoryLanguagesHelper
+  def repository_languages_bar(languages)
+    return if languages.none?
+
+    content_tag :div, class: 'progress repository-languages-bar' do
+      safe_join(languages.map { |lang| language_progress(lang) })
+    end
+  end
+
+  def language_progress(lang)
+    content_tag :div, nil,
+      class: "progress-bar has-tooltip",
+      style: "width: #{lang.share}%; background-color:#{lang.color}",
+      title: lang.name
+  end
+end
diff --git a/app/models/namespace.rb b/app/models/namespace.rb
index c1dc2f55346..de06e080a7d 100644
--- a/app/models/namespace.rb
+++ b/app/models/namespace.rb
@@ -122,6 +122,7 @@ class Namespace < ActiveRecord::Base
   def to_param
     full_path
   end
+  alias_method :flipper_id, :to_param
 
   def human_name
     owner_name
diff --git a/app/models/programming_language.rb b/app/models/programming_language.rb
new file mode 100644
index 00000000000..400d6c407a7
--- /dev/null
+++ b/app/models/programming_language.rb
@@ -0,0 +1,4 @@
+class ProgrammingLanguage < ActiveRecord::Base
+  validates :name, presence: true
+  validates :color, allow_blank: false, color: true
+end
diff --git a/app/models/project.rb b/app/models/project.rb
index da30d2fbb4f..af32afc08e2 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -192,6 +192,7 @@ class Project < ActiveRecord::Base
   has_many :hooks, class_name: 'ProjectHook'
   has_many :protected_branches
   has_many :protected_tags
+  has_many :repository_languages, -> { order "share DESC" }
 
   has_many :project_authorizations
   has_many :authorized_users, through: :project_authorizations, source: :user, class_name: 'User'
diff --git a/app/models/repository.rb b/app/models/repository.rb
index 50f42be661b..9a6281bc1f7 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -235,6 +235,12 @@ class Repository
     false
   end
 
+  def languages
+    return [] if empty?
+
+    raw_repository.languages(root_ref)
+  end
+
   # Makes sure a commit is kept around when Git garbage collection runs.
   # Git GC will delete commits from the repository that are no longer in any
   # branches or tags, but we want to keep some of these commits around, for
@@ -432,6 +438,8 @@ class Repository
   # Runs code after a repository has been forked/imported.
   def after_import
     expire_content_cache
+
+    DetectRepositoryLanguagesWorker.perform_async(project.id, project.owner.id)
   end
 
   # Runs code after a new commit has been pushed.
diff --git a/app/models/repository_language.rb b/app/models/repository_language.rb
new file mode 100644
index 00000000000..f467d4eafa3
--- /dev/null
+++ b/app/models/repository_language.rb
@@ -0,0 +1,12 @@
+class RepositoryLanguage < ActiveRecord::Base
+  belongs_to :project
+  belongs_to :programming_language
+
+  default_scope { includes(:programming_language) }
+
+  validates :project, presence: true
+  validates :share, inclusion: { in: 0..100, message: "The share of a lanuage is between 0 and 100" }
+  validates :programming_language, uniqueness: { scope: :project_id }
+
+  delegate :name, :color, to: :programming_language
+end
diff --git a/app/services/git_push_service.rb b/app/services/git_push_service.rb
index e3640e38bfa..637c1df4ad9 100644
--- a/app/services/git_push_service.rb
+++ b/app/services/git_push_service.rb
@@ -85,6 +85,8 @@ class GitPushService < BaseService
 
         types = Gitlab::FileDetector.types_in_paths(paths.to_a)
       end
+
+      DetectRepositoryLanguagesWorker.perform_async(@project.id, current_user.id)
     else
       types = []
     end
diff --git a/app/services/projects/detect_repository_languages_service.rb b/app/services/projects/detect_repository_languages_service.rb
new file mode 100644
index 00000000000..6669830ac8c
--- /dev/null
+++ b/app/services/projects/detect_repository_languages_service.rb
@@ -0,0 +1,53 @@
+module Projects
+  class DetectRepositoryLanguagesService < BaseService
+    attr_reader :detected_repository_languages, :programming_languages
+
+    def execute
+      repository_languages = project.repository_languages
+      detection = Gitlab::LanguageDetection.new(repository, repository_languages)
+
+      matching_programming_languages = ensure_programming_languages(detection)
+
+      RepositoryLanguage.transaction do
+        project.repository_languages.where(programming_language_id: detection.deletions).delete_all
+
+        detection.updates.each do |update|
+          RepositoryLanguage
+            .arel_table.update_manager
+            .where(project_id: project.id)
+            .where(programming_language_id: update[:programming_language_id])
+            .set(share: update[:share])
+        end
+
+        Gitlab::Database.bulk_insert(
+          RepositoryLanguage.table_name,
+          detection.insertions(matching_programming_languages)
+        )
+      end
+
+      project.repository_languages.reload
+    end
+
+    private
+
+    def ensure_programming_languages(detection)
+      existing_languages = ProgrammingLanguage.where(name: detection.languages)
+      return existing_languages if detection.languages.size == existing_languages.size
+
+      missing_languages = detection.languages - existing_languages.map(&:name)
+      created_languages = missing_languages.map do |name|
+        create_language(name, detection.language_color(name))
+      end
+
+      existing_languages + created_languages
+    end
+
+    def create_language(name, color)
+      ProgrammingLanguage.transaction do
+        ProgrammingLanguage.where(name: name).first_or_create(color: color)
+      end
+    rescue ActiveRecord::RecordNotUnique
+      retry
+    end
+  end
+end
diff --git a/app/views/projects/show.html.haml b/app/views/projects/show.html.haml
index 803ecca48f7..e011851be78 100644
--- a/app/views/projects/show.html.haml
+++ b/app/views/projects/show.html.haml
@@ -18,10 +18,11 @@
 = render "home_panel"
 
 - if can?(current_user, :download_code, @project)
-  %nav.project-stats{ class: container_class }
+  %nav.project-stats{ class: [container_class, ("limit-container-width" unless fluid_layout)] }
     = render 'stat_anchor_list', anchors: @project.statistics_anchors(show_auto_devops_callout: show_auto_devops_callout)
     = render 'stat_anchor_list', anchors: @project.statistics_buttons(show_auto_devops_callout: show_auto_devops_callout)
-
+    - if Feature.enabled?(:repository_languages, @project.namespace.becomes(Namespace))
+      = repository_languages_bar(@project.repository_languages)
 
 %div{ class: [container_class, ("limit-container-width" unless fluid_layout)] }
   - if @project.archived?
diff --git a/app/workers/all_queues.yml b/app/workers/all_queues.yml
index f2651cb54ec..e8b9999f83b 100644
--- a/app/workers/all_queues.yml
+++ b/app/workers/all_queues.yml
@@ -123,3 +123,4 @@
 - repository_update_remote_mirror
 - create_note_diff_file
 - delete_diff_files
+- detect_repository_languages
diff --git a/app/workers/detect_repository_languages_worker.rb b/app/workers/detect_repository_languages_worker.rb
new file mode 100644
index 00000000000..537b8fd5963
--- /dev/null
+++ b/app/workers/detect_repository_languages_worker.rb
@@ -0,0 +1,33 @@
+class DetectRepositoryLanguagesWorker
+  include ApplicationWorker
+  include ExceptionBacktrace
+  include ExclusiveLeaseGuard
+
+  sidekiq_options retry: 1
+
+  LEASE_TIMEOUT = 300
+
+  attr_reader :project
+
+  def perform(project_id, user_id)
+    @project = Project.find_by(id: project_id)
+    user = User.find_by(id: user_id)
+    return unless project && user
+
+    return if Feature.disabled?(:repository_languages, project.namespace)
+
+    try_obtain_lease do
+      ::Projects::DetectRepositoryLanguagesService.new(project, user).execute
+    end
+  end
+
+  private
+
+  def lease_timeout
+    LEASE_TIMEOUT
+  end
+
+  def lease_key
+    "gitlab:detect_repository_languages:#{project.id}"
+  end
+end
diff --git a/changelogs/unreleased/zj-repository-languages.yml b/changelogs/unreleased/zj-repository-languages.yml
new file mode 100644
index 00000000000..c42ba60be29
--- /dev/null
+++ b/changelogs/unreleased/zj-repository-languages.yml
@@ -0,0 +1,5 @@
+---
+title: Show repository languages for projects
+merge_request: 19480
+author:
+type: added
diff --git a/config/sidekiq_queues.yml b/config/sidekiq_queues.yml
index 3c85cd07d46..fb7738a5536 100644
--- a/config/sidekiq_queues.yml
+++ b/config/sidekiq_queues.yml
@@ -77,3 +77,4 @@
   - [repository_remove_remote, 1]
   - [create_note_diff_file, 1]
   - [delete_diff_files, 1]
+  - [detect_repository_languages, 1]
diff --git a/db/migrate/20180531185349_add_repository_languages.rb b/db/migrate/20180531185349_add_repository_languages.rb
new file mode 100644
index 00000000000..bfcfb618c87
--- /dev/null
+++ b/db/migrate/20180531185349_add_repository_languages.rb
@@ -0,0 +1,28 @@
+class AddRepositoryLanguages < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    create_table(:programming_languages) do |t|
+      t.string :name, null: false
+      t.string :color, null: false
+      t.datetime_with_timezone :created_at, null: false
+    end
+
+    create_table(:repository_languages, id: false) do |t|
+      t.references :project, null: false, foreign_key: { on_delete: :cascade }
+      t.references :programming_language, null: false
+      t.float :share, null: false
+    end
+
+    add_index :programming_languages, :name, unique: true
+    add_index :repository_languages, [:project_id, :programming_language_id],
+      unique: true, name: "index_repository_languages_on_project_and_languages_id"
+  end
+
+  def down
+    drop_table :repository_languages
+    drop_table :programming_languages
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 6f3433c1003..769baa825a5 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -1502,6 +1502,14 @@ ActiveRecord::Schema.define(version: 20180726172057) do
   add_index "personal_access_tokens", ["token"], name: "index_personal_access_tokens_on_token", unique: true, using: :btree
   add_index "personal_access_tokens", ["user_id"], name: "index_personal_access_tokens_on_user_id", using: :btree
 
+  create_table "programming_languages", force: :cascade do |t|
+    t.string "name", null: false
+    t.string "color", null: false
+    t.datetime_with_timezone "created_at", null: false
+  end
+
+  add_index "programming_languages", ["name"], name: "index_programming_languages_on_name", unique: true, using: :btree
+
   create_table "project_authorizations", id: false, force: :cascade do |t|
     t.integer "user_id", null: false
     t.integer "project_id", null: false
@@ -1788,6 +1796,14 @@ ActiveRecord::Schema.define(version: 20180726172057) do
   add_index "remote_mirrors", ["last_successful_update_at"], name: "index_remote_mirrors_on_last_successful_update_at", using: :btree
   add_index "remote_mirrors", ["project_id"], name: "index_remote_mirrors_on_project_id", using: :btree
 
+  create_table "repository_languages", id: false, force: :cascade do |t|
+    t.integer "project_id", null: false
+    t.integer "programming_language_id", null: false
+    t.float "share", null: false
+  end
+
+  add_index "repository_languages", ["project_id", "programming_language_id"], name: "index_repository_languages_on_project_and_languages_id", unique: true, using: :btree
+
   create_table "resource_label_events", id: :bigserial, force: :cascade do |t|
     t.integer "action", null: false
     t.integer "issue_id"
@@ -2359,6 +2375,7 @@ ActiveRecord::Schema.define(version: 20180726172057) do
   add_foreign_key "push_event_payloads", "events", name: "fk_36c74129da", on_delete: :cascade
   add_foreign_key "releases", "projects", name: "fk_47fe2a0596", on_delete: :cascade
   add_foreign_key "remote_mirrors", "projects", on_delete: :cascade
+  add_foreign_key "repository_languages", "projects", on_delete: :cascade
   add_foreign_key "resource_label_events", "issues", on_delete: :cascade
   add_foreign_key "resource_label_events", "labels", on_delete: :nullify
   add_foreign_key "resource_label_events", "merge_requests", on_delete: :cascade
diff --git a/lib/feature.rb b/lib/feature.rb
index d27b2b0e72f..09c5ef3ad94 100644
--- a/lib/feature.rb
+++ b/lib/feature.rb
@@ -46,6 +46,10 @@ class Feature
       get(key).enabled?(thing)
     end
 
+    def disabled?(key, thing = nil)
+      !enabled?(key, thing)
+    end
+
     def enable(key, thing = true)
       get(key).enable(thing)
     end
diff --git a/lib/gitlab/import_export/import_export.yml b/lib/gitlab/import_export/import_export.yml
index da3667faf7a..f69f98a78a3 100644
--- a/lib/gitlab/import_export/import_export.yml
+++ b/lib/gitlab/import_export/import_export.yml
@@ -107,6 +107,7 @@ excluded_attributes:
     - :storage_version
     - :remote_mirror_available_overridden
     - :description_html
+    - :repository_languages
   snippets:
     - :expired_at
   merge_request_diff:
diff --git a/lib/gitlab/language_detection.rb b/lib/gitlab/language_detection.rb
new file mode 100644
index 00000000000..a41435fdb79
--- /dev/null
+++ b/lib/gitlab/language_detection.rb
@@ -0,0 +1,68 @@
+module Gitlab
+  class LanguageDetection
+    MAX_LANGUAGES = 5
+
+    def initialize(repository, repository_languages)
+      @repository = repository
+      @repository_languages = repository_languages
+    end
+
+    def languages
+      detection.keys
+    end
+
+    def language_color(name)
+      detection.dig(name, :color)
+    end
+
+    # Newly detected languages, returned in a structure accepted by
+    # Gitlab::Database.bulk_insert
+    def insertions(programming_languages)
+      lang_to_id = programming_languages.map { |p| [p.name, p.id] }.to_h
+
+      (languages - previous_language_names).map do |new_lang|
+        {
+          project_id: @repository.project.id,
+          share: detection[new_lang][:value],
+          programming_language_id: lang_to_id[new_lang]
+        }
+      end
+    end
+
+    # updates analyses which records only require updating of their share
+    def updates
+      to_update = @repository_languages.select do |lang|
+        detection.key?(lang.name) && detection[lang.name][:value] != lang.share
+      end
+
+      to_update.map do |lang|
+        { programming_language_id: lang.programming_language_id, share: detection[lang.name][:value] }
+      end
+    end
+
+    # Returns the ids of the programming languages that do not occur in the detection
+    # as current repository languages
+    def deletions
+      @repository_languages.map do |repo_lang|
+        next if detection.key?(repo_lang.name)
+
+        repo_lang.programming_language_id
+      end.compact
+    end
+
+    private
+
+    def previous_language_names
+      @previous_language_names ||= @repository_languages.map(&:name)
+    end
+
+    def detection
+      @detection ||=
+        @repository
+        .languages
+        .first(MAX_LANGUAGES)
+        .map { |l| [l[:label], l] }
+        .to_h
+    end
+  end
+end
diff --git a/spec/factories/programming_languages.rb b/spec/factories/programming_languages.rb
new file mode 100644
index 00000000000..d3511d42b6c
--- /dev/null
+++ b/spec/factories/programming_languages.rb
@@ -0,0 +1,6 @@
+FactoryBot.define do
+  factory :programming_language do
+    name 'Ruby'
+    color '#123456'
+  end
+end
diff --git a/spec/factories/repository_languages.rb b/spec/factories/repository_languages.rb
new file mode 100644
index 00000000000..1757ba6766c
--- /dev/null
+++ b/spec/factories/repository_languages.rb
@@ -0,0 +1,7 @@
+FactoryBot.define do
+  factory :repository_language do
+    project
+    programming_language
+    share 98.5
+  end
+end
diff --git a/spec/lib/gitlab/import_export/all_models.yml b/spec/lib/gitlab/import_export/all_models.yml
index c175dc1e4dd..b3e3ead9c5e 100644
--- a/spec/lib/gitlab/import_export/all_models.yml
+++ b/spec/lib/gitlab/import_export/all_models.yml
@@ -297,6 +297,7 @@ project:
 - settings
 - ci_cd_settings
 - import_export_upload
+- repository_languages
 award_emoji:
 - awardable
 - user
diff --git a/spec/lib/gitlab/language_detection_spec.rb b/spec/lib/gitlab/language_detection_spec.rb
new file mode 100644
index 00000000000..9636fbd401b
--- /dev/null
+++ b/spec/lib/gitlab/language_detection_spec.rb
@@ -0,0 +1,85 @@
+require 'spec_helper'
+
+describe Gitlab::LanguageDetection do
+  set(:project) { create(:project, :repository) }
+  set(:ruby) { create(:programming_language, name: 'Ruby') }
+  set(:haskell) { create(:programming_language, name: 'Haskell') }
+  let(:repository) { project.repository }
+  let(:detection) do
+    [{ value: 66.63, label: "Ruby", color: "#701516", highlight: "#701516" },
+     { value: 12.96, label: "JavaScript", color: "#f1e05a", highlight: "#f1e05a" },
+     { value: 7.9, label: "Elixir", color: "#e34c26", highlight: "#e34c26" },
+     { value: 2.51, label: "CoffeeScript", color: "#244776", highlight: "#244776" },
+     { value: 1.51, label: "Go", color: "#2a4776", highlight: "#244776" },
+     { value: 1.1, label: "MepmepLang", color: "#2a4776", highlight: "#244776" }]
+  end
+  let(:repository_languages) do
+    [RepositoryLanguage.new(share: 10, programming_language: ruby)]
+  end
+
+  subject { described_class.new(repository, repository_languages) }
+
+  before do
+    allow(repository).to receive(:languages).and_return(detection)
+  end
+
+  describe '#languages' do
+    it 'returns the language names' do
+      expect(subject.languages).to eq(%w[Ruby JavaScript Elixir CoffeeScript Go])
+    end
+  end
+
+  describe '#insertions' do
+    let(:programming_languages) { [ruby, haskell] }
+    let(:detection) do
+      [{ value: 10, label: haskell.name, color: haskell.color }]
+    end
+
+    it 'only includes new languages' do
+      insertions = subject.insertions(programming_languages)
+
+      expect(insertions).not_to be_empty
+      expect(insertions.first[:project_id]).to be(project.id)
+      expect(insertions.first[:programming_language_id]).to be(haskell.id)
+      expect(insertions.first[:share]).to be(10)
+    end
+  end
+
+  describe '#updates' do
+    it 'updates the share of languages' do
+      first_update = subject.updates.first
+
+      expect(first_update).not_to be_nil
+      expect(first_update[:programming_language_id]).to eq(ruby.id)
+      expect(first_update[:share]).to eq(66.63)
+    end
+
+    it 'does not include languages to be removed' do
+      ids = subject.updates.map { |h| h[:programming_language_id] }
+
+      expect(ids).not_to include(haskell.id)
+    end
+
+    context 'when silent writes occur' do
+      let(:repository_languages) do
+        [RepositoryLanguage.new(share: 66.63, programming_language: ruby)]
+      end
+
+      it "doesn't include them in the result" do
+        expect(subject.updates).to be_empty
+      end
+    end
+  end
+
+  describe '#deletions' do
+    let(:repository_languages) do
+      [RepositoryLanguage.new(share: 10, programming_language: ruby),
+       RepositoryLanguage.new(share: 5, programming_language: haskell)]
+    end
+
+    it 'lists undetected languages' do
+      expect(subject.deletions).not_to be_empty
+      expect(subject.deletions).to include(haskell.id)
+    end
+  end
+end
diff --git a/spec/models/programming_language_spec.rb b/spec/models/programming_language_spec.rb
new file mode 100644
index 00000000000..99cd358f863
--- /dev/null
+++ b/spec/models/programming_language_spec.rb
@@ -0,0 +1,11 @@
+require 'spec_helper'
+
+describe ProgrammingLanguage do
+  it { is_expected.to respond_to(:name) }
+  it { is_expected.to respond_to(:color) }
+
+  it { is_expected.to validate_presence_of(:name) }
+  it { is_expected.to allow_value("#000000").for(:color) }
+  it { is_expected.not_to allow_value("000000").for(:color) }
+  it { is_expected.not_to allow_value("#0z0000").for(:color) }
+end
diff --git a/spec/models/project_spec.rb b/spec/models/project_spec.rb
index ef4167a3912..340d2d95500 100644
--- a/spec/models/project_spec.rb
+++ b/spec/models/project_spec.rb
@@ -69,6 +69,7 @@ describe Project do
     it { is_expected.to have_many(:pages_domains) }
     it { is_expected.to have_many(:labels).class_name('ProjectLabel') }
     it { is_expected.to have_many(:users_star_projects) }
+    it { is_expected.to have_many(:repository_languages) }
     it { is_expected.to have_many(:environments) }
     it { is_expected.to have_many(:deployments) }
     it { is_expected.to have_many(:todos) }
diff --git a/spec/models/repository_language_spec.rb b/spec/models/repository_language_spec.rb
new file mode 100644
index 00000000000..e2e4beb512f
--- /dev/null
+++ b/spec/models/repository_language_spec.rb
@@ -0,0 +1,16 @@
+require 'spec_helper'
+
+describe RepositoryLanguage do
+  let(:repository_language) { build(:repository_language) }
+
+  describe 'associations' do
+    it { is_expected.to belong_to(:project) }
+    it { is_expected.to belong_to(:programming_language) }
+  end
+
+  describe 'validations' do
+    it { is_expected.to allow_value(0).for(:share) }
+    it { is_expected.to allow_value(100.0).for(:share) }
+    it { is_expected.not_to allow_value(100.1).for(:share) }
+  end
+end
diff --git a/spec/services/git_push_service_spec.rb b/spec/services/git_push_service_spec.rb
index 657afb2b2b5..a3c9a660c2f 100644
--- a/spec/services/git_push_service_spec.rb
+++ b/spec/services/git_push_service_spec.rb
@@ -3,8 +3,8 @@ require 'spec_helper'
 describe GitPushService, services: true do
   include RepoHelpers
 
-  let(:user)     { create(:user) }
-  let(:project)  { create(:project, :repository) }
+  set(:user)     { create(:user) }
+  set(:project)  { create(:project, :repository) }
   let(:blankrev) { Gitlab::Git::BLANK_SHA }
   let(:oldrev)   { sample_commit.parent_id }
   let(:newrev)   { sample_commit.id }
diff --git a/spec/services/projects/detect_repository_languages_service_spec.rb b/spec/services/projects/detect_repository_languages_service_spec.rb
new file mode 100644
index 00000000000..f90d558938f
--- /dev/null
+++ b/spec/services/projects/detect_repository_languages_service_spec.rb
@@ -0,0 +1,54 @@
+require 'spec_helper'
+
+describe Projects::DetectRepositoryLanguagesService, :clean_gitlab_redis_shared_state do
+  set(:project) { create(:project, :repository) }
+
+  subject { described_class.new(project, project.owner) }
+
+  before do
+    allow(Feature).to receive(:disabled?).and_return(false)
+  end
+
+  describe '#execute' do
+    context 'without previous detection' do
+      it 'inserts new programming languages in the database' do
+        subject.execute
+
+        expect(ProgrammingLanguage.exists?(name: 'Ruby')).to be(true)
+        expect(ProgrammingLanguage.count).to be(4)
+      end
+
+      it 'inserts the repository langauges' do
+        names = subject.execute.map(&:name)
+
+        expect(names).to eq(%w[Ruby JavaScript HTML CoffeeScript])
+      end
+    end
+
+    context 'with a previous detection' do
+      before do
+        subject.execute
+
+        allow(project.repository).to receive(:languages).and_return(
+          [{ value: 99.63, label: "Ruby", color: "#701516", highlight: "#701516" },
+           { value: 0.3, label: "D", color: "#701516", highlight: "#701516" }]
+        )
+      end
+
+      it 'updates the repository languages' do
+        repository_languages = subject.execute.map(&:name)
+
+        expect(repository_languages).to eq(%w[Ruby D])
+      end
+    end
+
+    context 'when no repository exists' do
+      set(:project) { create(:project) }
+
+      it 'has no languages' do
+        expect(subject.execute).to be_empty
+        expect(project.repository_languages).to be_empty
+      end
+    end
+  end
+end
diff --git a/spec/workers/detect_repository_languages_worker_spec.rb b/spec/workers/detect_repository_languages_worker_spec.rb
new file mode 100644
index 00000000000..ff3878fbc8e
--- /dev/null
+++ b/spec/workers/detect_repository_languages_worker_spec.rb
@@ -0,0 +1,32 @@
+require 'spec_helper'
+
+describe DetectRepositoryLanguagesWorker do
+  set(:project) { create(:project) }
+  let(:user) { project.owner }
+
+  subject { described_class.new }
+
+  describe '#perform' do
+    it 'calls de DetectRepositoryLanguages service' do
+      service = double
+      allow(::Projects::DetectRepositoryLanguagesService).to receive(:new).and_return(service)
+      expect(service).to receive(:execute)
+
+      subject.perform(project.id, user.id)
+    end
+
+    context 'when invalid ids are used' do
+      it 'does not raise when the project could not be found' do
+        expect do
+          subject.perform(-1, user.id)
+        end.not_to raise_error
+      end
+
+      it 'does not raise when the user could not be found' do
+        expect do
+          subject.perform(project.id, -1)
+        end.not_to raise_error
+      end
+    end
+  end
+end