How to internationalize a Rails app?

Internationalizing a Rails app means preparing it for multiple languages, ensuring users across different regions can engage with it in their preferred language. Here’s how you can internationalize a Rails application:

1. Use the I18n Library: Rails comes with a built-in internationalization (I18n) framework that allows you to externalize strings in your application. Initialize it by setting a default locale in `config/application.rb` like so: `config.i18n.default_locale = :en`.

2. Store Translations: Create YAML files under `config/locales` to store translations. For example, `en.yml` for English, `es.yml` for Spanish, and so forth. Within these files, you define key-value pairs where the key remains constant, but the value changes based on the language.

3. Externalize Strings: Replace hard-coded strings in views, controllers, and models with calls like `I18n.t(‘greeting’)`. Here, `’greeting’` would be a key in your YAML translation file.

4. Use Locale with URLs: To provide a localized experience, you can set up your routes to include the locale. For instance, URLs can be structured as `/en/products` or `/es/products`. The locale can then be extracted in your controllers to serve appropriate content.

5. Pluralization: The I18n framework supports pluralization. For languages with multiple plural forms, you can specify them in your YAML files and use them in your views.

6. Date, Time, and Currency Formatting: Different regions have varying conventions for date, time, and currency. Rails I18n supports these variations, allowing you to present data in a way that feels native to each audience.

7. Fallbacks: Sometimes a translation might be missing for a specific language. Configure fallbacks in `config/application.rb` using `config.i18n.fallbacks = [:default_locale]` to ensure the application still provides information in such cases.

8. Leverage Gems: There are several gems like `globalize` that extend the I18n functionalities, helping manage model content translations or even automate translations.

Rails offers a comprehensive set of tools for internationalizing an app. When building for a global audience, ensure translations are accurate, culturally appropriate, and continuously updated.