Refactor i18n setup and improve structure for maintainability

- Relocated `i18n` configuration files to `src/lib/i18n` for better organization.
- Removed obsolete `request.ts` and `routing.ts` files, simplifying `i18n` setup within the project.
- Added extensive tests for `i18n/utils` to validate locale-related utilities, including locale name, native name, and flag retrieval.
- Introduced a detailed `I18N_IMPLEMENTATION_PLAN.md` to document implementation phases, decisions, and recommendations for future extensions.
- Enhanced TypeScript definitions and modularity across i18n utilities for improved developer experience.

frontend/src/lib/i18n/request.ts

@@ -14,7 +14,7 @@
  */
 
 import { getRequestConfig } from 'next-intl/server';
-import { routing } from './routing';
+import { routing } from '@/lib/i18n/routing';
 
 export default getRequestConfig(async ({ locale }) => {
   // Validate that the incoming `locale` parameter is valid

frontend/src/lib/i18n/utils.ts

@@ -2,11 +2,10 @@
 /**
  * Utility functions for internationalization.
  *
- * This file demonstrates type-safe translation usage.
+ * This file provides pure utility functions for i18n without React dependencies.
+ * For React hooks, see hooks.ts
  */
 
-import { useTranslations } from 'next-intl';
-
 /**
  * Get the display name for a locale code.
  *
@@ -54,28 +53,6 @@ export function getLocaleFlag(locale: string): string {
   return flags[locale] || flags.en;
 }
 
-/**
- * Hook to get common translations.
- * This demonstrates type-safe usage of useTranslations.
- *
- * @returns Object with commonly used translation functions
- */
-export function useCommonTranslations() {
-  const t = useTranslations('common');
-
-  return {
-    loading: () => t('loading'),
-    error: () => t('error'),
-    success: () => t('success'),
-    cancel: () => t('cancel'),
-    save: () => t('save'),
-    delete: () => t('delete'),
-    edit: () => t('edit'),
-    close: () => t('close'),
-    confirm: () => t('confirm'),
-  };
-}
-
 /**
  * Format a relative time string (e.g., "2 hours ago").
  * This is a placeholder for future implementation with next-intl's date/time formatting.

frontend/src/middleware.ts

@@ -1,7 +1,7 @@
 import { NextResponse } from 'next/server';
 import type { NextRequest } from 'next/server';
 import createMiddleware from 'next-intl/middleware';
-import { routing } from './i18n/routing';
+import { routing } from './lib/i18n/routing';
 
 // Create next-intl middleware for locale handling
 const intlMiddleware = createMiddleware(routing);