✨ feat(translations): chinese translations (#316)

* ✨ feat(translations): chinese translations

* ✨ feat(App.vue): append dropdown item

frontend/src/lang/index.js

@@ -3,6 +3,7 @@ import de from './translations/de.json';
 import ru from './translations/ru.json';
 import en from './translations/en.json';
 import vi from './translations/vi.json';
+import zh from './translations/zh.json';
 import {createI18n} from "vue-i18n";
 
 // Create i18n instance with options
@@ -20,7 +21,8 @@ const i18n = createI18n({
     "de": de,
     "ru": ru,
     "en": en,
-    "vi": vi
+    "vi": vi,
+    "zh": zh
   }
 });