Add Japanese (ja) locale files and update type definition for supported locales (#1726)

* feat: add locale files for Japanese (ja)

* fix: update locale type definition to include all supported languages

src/i18n.ts

@@ -2,6 +2,7 @@ import { createI18n } from 'vue-i18n'
 import en from './locales/en'
 import zh from './locales/zh'
 import ru from './locales/ru'
+import ja from './locales/ja'
 
 export const i18n = createI18n({
   // Must set `false`, as Vue I18n Legacy API is for Vue 2
@@ -11,6 +12,7 @@ export const i18n = createI18n({
   messages: {
     en,
     zh,
-    ru
+    ru,
+    ja
   }
 })