I18n: Automatically choose locale through HTTP header

Gemfile

@@ -14,6 +14,7 @@ gem 'faraday-net_http_persistent'
 gem 'faye-websocket'
 gem 'forgery'
 gem 'highline'
+gem 'http_accept_language'
 gem 'i18n-js'
 gem 'ims-lti', '< 2.0.0' # Version 2 implements LTI 2.0, which is deprecated. Hence, we stay with version 1.
 gem 'jbuilder'

Gemfile.lock

@@ -181,6 +181,7 @@ GEM
     http-accept (1.7.0)
     http-cookie (1.0.5)
       domain_name (~> 0.5)
+    http_accept_language (2.1.1)
     i18n (1.12.0)
       concurrent-ruby (~> 1.0)
     i18n-js (4.2.0)
@@ -561,6 +562,7 @@ DEPENDENCIES
   forgery
   headless
   highline
+  http_accept_language
   i18n-js
   ims-lti (< 2.0.0)
   jbuilder

app/controllers/application_controller.rb

@@ -122,7 +122,7 @@ class ApplicationController < ActionController::Base
 
   def switch_locale(&)
     session[:locale] = sanitize_locale(params[:custom_locale] || params[:locale] || session[:locale])
-    locale = session[:locale] || I18n.default_locale
+    locale = session[:locale] || http_accept_language.compatible_language_from(I18n.available_locales) || I18n.default_locale
     Sentry.set_extras(locale:)
     I18n.with_locale(locale, &)
   end