feat: i18n locales lazy loading (#482)

Co-authored-by: Anthony Fu <anthonyfu117@hotmail.com>

src/components/TheFooter.vue

@@ -1,10 +1,14 @@
 <script setup lang="ts">
-const { t, availableLocales, locale } = useI18n()
+import { availableLocales, loadLanguageAsync } from '~/modules/i18n'
 
-const toggleLocales = () => {
+const { t, locale } = useI18n()
+
+const toggleLocales = async () => {
   // change to some real logic
   const locales = availableLocales
-  locale.value = locales[(locales.indexOf(locale.value) + 1) % locales.length]
+  const newLocale = locales[(locales.indexOf(locale.value) + 1) % locales.length]
+  await loadLanguageAsync(newLocale)
+  locale.value = newLocale
 }
 </script>
 

src/modules/i18n.ts

@@ -1,3 +1,4 @@
+import type { Locale } from 'vue-i18n'
 import { createI18n } from 'vue-i18n'
 import { type UserModule } from '~/types'
 
@@ -5,21 +6,45 @@ import { type UserModule } from '~/types'
 // https://vitejs.dev/guide/features.html#glob-import
 //
 // Don't need this? Try vitesse-lite: https://github.com/antfu/vitesse-lite
-const messages = Object.fromEntries(
-  Object.entries(
-    import.meta.glob<{ default: any }>('../../locales/*.y(a)?ml', { eager: true }))
-    .map(([key, value]) => {
-      const yaml = key.endsWith('.yaml')
-      return [key.slice(14, yaml ? -5 : -4), value.default]
-    }),
-)
+const i18n = createI18n({
+  legacy: false,
+  locale: '',
+  messages: {},
+})
+
+const localesMap = Object.fromEntries(
+  Object.entries(import.meta.glob('../../locales/*.yml'))
+    .map(([path, loadLocale]) => [path.match(/([\w-]*)\.yml$/)?.[1], loadLocale]),
+) as Record<Locale, () => Promise<{ default: Record<string, string> }>>
+
+export const availableLocales = Object.keys(localesMap)
+
+const loadedLanguages: string[] = []
+
+function setI18nLanguage(lang: Locale) {
+  i18n.global.locale.value = lang as any
+  if (typeof document !== 'undefined')
+    document.querySelector('html')?.setAttribute('lang', lang)
+  return lang
+}
+
+export async function loadLanguageAsync(lang: string): Promise<Locale> {
+  // If the same language
+  if (i18n.global.locale.value === lang)
+    return setI18nLanguage(lang)
+
+  // If the language was already loaded
+  if (loadedLanguages.includes(lang))
+    return setI18nLanguage(lang)
+
+  // If the language hasn't been loaded yet
+  const messages = await localesMap[lang]()
+  i18n.global.setLocaleMessage(lang, messages.default)
+  loadedLanguages.push(lang)
+  return setI18nLanguage(lang)
+}
 
 export const install: UserModule = ({ app }) => {
-  const i18n = createI18n({
-    legacy: false,
-    locale: 'en',
-    messages,
-  })
-
   app.use(i18n)
+  loadLanguageAsync('en')
 }