Replace Status#translatable? with language matrix in separate endpoint (#24037)

app/controllers/api/v1/instances/translation_languages_controller.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class Api::V1::Instances::TranslationLanguagesController < Api::BaseController
+  skip_before_action :require_authenticated_user!, unless: :whitelist_mode?
+
+  before_action :set_languages
+
+  def show
+    expires_in 1.day, public: true
+    render json: @languages
+  end
+
+  private
+
+  def set_languages
+    if TranslationService.configured?
+      @languages = Rails.cache.fetch('translation_service/languages', expires_in: 7.days, race_condition_ttl: 1.hour) { TranslationService.configured.languages }
+      @languages['und'] = @languages.delete(nil) if @languages.key?(nil)
+    else
+      @languages = {}
+    end
+  end
+end