fix: components not updating correctly when changing language /2

Fixes :
- lacking i18n.global.locale.value in datetime.ts
- remove a test in i18n.ts that was always false in past versions of the code because i18n.global.locale is an object and lang is a string
- correctly type createI18n with <false> for legacy to solve wrong TypeScript error (see https://github.com/intlify/vue-i18n/issues/785, https://github.com/intlify/vue-i18n/issues/889#issuecomment-1017250573)

Fixes: #1597, #1772, and possibly other related issues.

src/filters/datetime.ts

@@ -79,7 +79,7 @@ function formatDateTimeString(
   return format.format(parseDateTime(value));
 }
 
-const locale = () => i18n.global.locale.replace("_", "-");
+const locale = () => i18n.global.locale.value.replace("_", "-");
 
 export {
   formatDateISOStringWithoutTime,

src/utils/i18n.ts

@@ -26,7 +26,7 @@ export const locale =
     ? language
     : language.split("-")[0];
 
-export const i18n = createI18n({
+export const i18n = createI18n<false>({
   legacy: false,
   locale: locale, // set locale
   // eslint-disable-next-line @typescript-eslint/ban-ts-comment
@@ -77,11 +77,6 @@ function vueI18NfileForLanguage(lang: string) {
 }
 
 export async function loadLanguageAsync(lang: string): Promise<string> {
-  // If the same language
-  if (i18n.global.locale === lang) {
-    return Promise.resolve(setI18nLanguage(lang));
-  }
-
   // If the language was already loaded
   if (loadedLanguages.includes(lang)) {
     return Promise.resolve(setI18nLanguage(lang));