What is CodeIgniter 4's Language/Localization system?

CodeIgniter 4's Language system provides internationalization (i18n) support. Create language files in app/Language/en/Messages.php: return ["welcome" => "Welcome, {0}!", "not_found" => "Page not found"]. Load language strings: $lang = service("language")->setLocale("fr"). Get a string: lang("Messages.welcome", ["Alice"]) — placeholders {0}, {1} are replaced with arguments. In views: <?= lang("Messages.welcome", [$username]) ?>. Auto-detect locale from browser: $request->negotiate->language(["en", "fr", "de"]). Store locale in session for user preference persistence. Language files can be nested: lang("Messages.validation.required"). CI4's language system is simpler than Laravel's but sufficient for most multi-language applications. For complex pluralization and number formatting, consider adding the intl PHP extension.