feat(i18n): enhance language management by saving user preference and auto detect browser language (#487)

* feat(i18n): enhance language management by saving user preference and detecting browser language

- Added a watcher to save the selected language to localStorage on change.
- Implemented browser language detection to set the default language based on user settings or browser preferences.

* use ~/utils/localstorage, remove setting savedLang in mounted as this is already set in i18.ts.

* do not repeat fallbackLocale and remove console log.

---------

Co-authored-by: Miroslav Šedivý <sedivy.miro@gmail.com>

client/src/components/menu.vue

@@ -60,8 +60,9 @@
 </style>
 
 <script lang="ts">
-  import { Component, Vue } from 'vue-property-decorator'
+  import { Component, Vue, Watch } from 'vue-property-decorator'
   import { messages } from '~/locale'
+  import { set } from '~/utils/localstorage'
 
   @Component({ name: 'neko-menu' })
   export default class extends Vue {
@@ -77,6 +78,11 @@
       this.$accessor.client.toggleAbout()
     }
 
+    @Watch('$i18n.locale')
+    onLanguageChange(newLang: string) {
+      set('lang', newLang)
+    }
+
     mounted() {
       const default_lang = new URL(location.href).searchParams.get('lang')
       if (default_lang && this.langs.includes(default_lang)) {

client/src/plugins/i18n.ts

@@ -1,11 +1,31 @@
 import Vue from 'vue'
 import VueI18n from 'vue-i18n'
 import { messages } from '~/locale'
+import { get } from '~/utils/localstorage'
 
 Vue.use(VueI18n)
 
+const fallbackLocale = 'en'
+
+function detectBrowserLanguage(): string {
+  const browserLang = navigator.language.toLowerCase()
+
+  const supportedLangs = Object.keys(messages)
+  if (supportedLangs.includes(browserLang)) {
+    return browserLang
+  }
+
+  const baseLang = browserLang.split('-')[0]
+  const matchingLang = supportedLangs.find((lang) => lang.startsWith(baseLang))
+  if (matchingLang) {
+    return matchingLang
+  }
+
+  return fallbackLocale
+}
+
 export const i18n = new VueI18n({
-  locale: 'en',
+  locale: get<string>('lang', detectBrowserLanguage()),
-  fallbackLocale: 'en',
+  fallbackLocale,
   messages,
 })