feat(translation): improve translation fallback mechanism

Enhance the translation retrieval process by adding the fallback locale
from the runtime configuration. This ensures that if the current locale
and other sources do not yield a translation, the fallback locale is
considered, improving the robustness of the translation system.

packages/core/src/translation.ts

@@ -105,7 +105,7 @@ export function useTranslationHelper() {
 
       if (!result) {
         result = findTranslation<T>(routeLocaleCache[cacheKey] || null, key)
-        ?? findTranslation<T>(generalLocaleCache[locale] || null, key)
+          ?? findTranslation<T>(generalLocaleCache[locale] || null, key)
       }
 
       if (result) {

src/runtime/translation-server-middleware.ts

@@ -2,6 +2,7 @@ import type { H3Event } from 'h3'
 import { getQuery, getCookie } from 'h3'
 import { interpolate, useTranslationHelper } from 'nuxt-i18n-micro-core'
 import type { Params, Translations } from 'nuxt-i18n-micro-types'
+import { useRuntimeConfig } from '#imports'
 
 async function fetchTranslations(locale: string): Promise<Translations> {
   try {
@@ -16,13 +17,15 @@ async function fetchTranslations(locale: string): Promise<Translations> {
 
 export const useTranslationServerMiddleware = async (event: H3Event, defaultLocale?: string, currentLocale?: string) => {
   const { getTranslation, loadTranslations, hasGeneralTranslation } = useTranslationHelper()
+  const config = useRuntimeConfig(event).i18nConfig
 
   const locale = (
     currentLocale
     || event.context.params?.locale
     || getQuery(event)?.locale
     || getCookie(event, 'user-locale')
     || event.headers.get('accept-language')?.split(',')[0]
+    || config.fallbackLocale
     || defaultLocale
     || 'en').toString()