Add vi-VN language support

Resolve #8975

CHANGELOG.md

@@ -12,6 +12,7 @@ You should also include the user name that made the change.
 ## 12.x.x (unreleased)
 
 ### Improvements
+- Client: Add vi-VN language support
 
 ### Bugfixes
 - Client: 一度作ったwebhookの設定画面を開こうとするとページがフリーズする @syuilo

locales/index.js

@@ -36,6 +36,7 @@ const languages = [
 	'sk-SK',
 	'ug-CN',
 	'uk-UA',
+	'vi-VN',
 	'zh-CN',
 	'zh-TW',
 ];