Pass default values for `translate` through I18n

A default value can be a string that needs interpolation, Hash that
needs resolution via the `:count` option, or a Proc that needs
evaluation.  Therefore, pass default values through `I18n.translate` to
handle these cases.

Fixes #26032.
Fixes #41277.
Fixes #41380.

actionview/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   The `translate` helper now passes `default` values that aren't
+    translation keys through `I18n.translate` for interpolation.
+
+    *Jonathan Hefner*
+
 *   Adds option `extname` to `stylesheet_link_tag` to skip default
     `.css` extension appended to the stylesheet path.
 

actionview/lib/action_view/helpers/translation_helper.rb

@@ -93,7 +93,9 @@ module ActionView
             break translated unless translated.equal?(MISSING_TRANSLATION)
           end
 
-          break alternatives.first if alternatives.present? && !alternatives.first.is_a?(Symbol)
+          if alternatives.present? && !alternatives.first.is_a?(Symbol)
+            break alternatives.first && I18n.translate(**options, default: alternatives)
+          end
 
           first_key ||= key
           key = alternatives&.shift

actionview/test/template/translation_helper_test.rb

@@ -158,11 +158,6 @@ class TranslationHelperTest < ActiveSupport::TestCase
     I18n.exception_handler = old_exception_handler
   end
 
-  def test_hash_default
-    default = { separator: ".", delimiter: "," }
-    assert_equal default, translate(:'special.number.format', default: default)
-  end
-
   def test_translation_returning_an_array
     expected = %w(foo bar)
     assert_equal expected, translate(:"translations.array")
@@ -328,6 +323,27 @@ class TranslationHelperTest < ActiveSupport::TestCase
     assert_equal "A Generic String", translation
   end
 
+  def test_translate_with_interpolated_string_default
+    translation = translate(:"translations.missing", default: "An %{kind} String", kind: "Interpolated")
+    assert_equal "An Interpolated String", translation
+  end
+
+  def test_translate_with_hash_default
+    hash = { one: "%{count} thing", other: "%{count} things" }
+    assert_equal hash, translate(:"translations.missing", default: hash)
+  end
+
+  def test_translate_with_hash_default_and_count
+    hash = { one: "%{count} thing", other: "%{count} things" }
+    assert_equal "1 thing", translate(:"translations.missing", default: hash, count: 1)
+    assert_equal "2 things", translate(:"translations.missing", default: hash, count: 2)
+  end
+
+  def test_translate_with_proc_default
+    translation = translate(:"translations.missing", default: Proc.new { "From Proc" })
+    assert_equal "From Proc", translation
+  end
+
   def test_translate_with_object_default
     translation = translate(:'translations.missing', default: 123)
     assert_equal 123, translation