fix: scope locale to request via around_action

Author: AndreyHirsa

.ruby-version

@@ -1 +1 @@
-3.3.0
+3.3.6

Gemfile

@@ -5,8 +5,8 @@ ruby ">= 3.1"
 gem "rails", "~> 7.2.0"
 gem "puma", ">= 5.0"
 gem "bootsnap", require: false
-gem "tzinfo-data", platforms: %i[windows jruby]
+gem "tzinfo-data", platforms: %i[mingw mswin x64_mingw jruby]
 
 group :development do
-  gem "debug", platforms: %i[mri windows]
+  gem "debug", platforms: %i[mri mingw mswin x64_mingw]
 end

README.md

@@ -8,7 +8,7 @@ Demonstrates automated localization for a Ruby on Rails app that authors UI stri
 
 - `config/locales/en.yml` – source UI strings (English)
 - `config/locales/{es,fr,de}.yml` – translated catalogs, generated by Lingo.dev
-- `app/controllers/application_controller.rb` – `set_locale` before_action that picks from URL param or `Accept-Language`
+- `app/controllers/application_controller.rb` – `switch_locale` around_action that picks from URL param or `Accept-Language`
 - `app/views/home/index.html.erb` – view demonstrating `t()` interpolation and pluralization
 - `i18n.json` – Lingo.dev CLI configuration (`yaml-root-key` bucket)
 - `.github/workflows/translate.yml` – GitHub Actions workflow
@@ -24,7 +24,7 @@ Demonstrates automated localization for a Ruby on Rails app that authors UI stri
 
 The Lingo.dev CLI reads `config/locales/en.yml`, identifies new or changed entries using a lockfile, translates the delta through a configured localization engine, and writes per-locale files (`es.yml`, `fr.yml`, `de.yml`) alongside the source. The locale root key (`en:` → `es:`), nested namespaces, `%{name}` interpolation, and plural categories (`zero`, `one`, `other`) are preserved – only translatable text changes. The GitHub Actions workflow runs this on every push to main.
 
-Rails' built-in i18n API loads every YAML file under `config/locales/` at boot. `ApplicationController#set_locale` picks the request locale from a URL parameter or the `Accept-Language` header, and views render translations with `t()` and `l()` helpers.
+Rails' built-in i18n API loads every YAML file under `config/locales/` at boot. `ApplicationController#switch_locale` picks the request locale from a URL parameter or the `Accept-Language` header and wraps the action in `I18n.with_locale`, so views render translations with `t()` and `l()` helpers without leaking the locale across requests.
 
 ## Locales
 

app/controllers/application_controller.rb

@@ -1,18 +1,16 @@
 class ApplicationController < ActionController::Base
-  before_action :set_locale
+  around_action :switch_locale
 
   private
 
-  def set_locale
-    I18n.locale = params[:locale] ||
-                  http_accept_locale ||
-                  I18n.default_locale
+  def switch_locale(&action)
+    locale = params[:locale] || http_accept_locale || I18n.default_locale
+    I18n.with_locale(locale, &action)
   end
 
   def http_accept_locale
-    request.env["HTTP_ACCEPT_LANGUAGE"]
-      &.scan(/[a-z]{2}/)
-      &.find { |l| I18n.available_locales.map(&:to_s).include?(l) }
+    header = request.headers["Accept-Language"].to_s
+    header.scan(/[a-z]{2}/).find { |l| I18n.available_locales.map(&:to_s).include?(l) }
   end
 
   def default_url_options

app/views/layouts/application.html.erb

@@ -166,7 +166,7 @@
       <div class="wordmark"><%= t("app.title") %></div>
       <nav class="lang-switcher">
         <% I18n.available_locales.each do |locale| %>
-          <%= link_to locale.upcase, url_for(locale: locale), class: (I18n.locale == locale ? "active" : nil) %>
+          <%= link_to locale.upcase, url_for(locale: locale), class: ("active" if I18n.locale == locale) %>
         <% end %>
       </nav>
     </header>

config/application.rb

@@ -6,7 +6,7 @@
 
 Bundler.require(*Rails.groups)
 
-module RailsLocalizationExample
+module RubyOnRailsLocalizationExample
   class Application < Rails::Application
     config.load_defaults 7.2
 

config/boot.rb

@@ -1,4 +1,4 @@
 ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../Gemfile", __dir__)
 
 require "bundler/setup"
-require "bootsnap/setup" if File.exist?(File.expand_path("../Gemfile.lock", __dir__))
+require "bootsnap/setup"