Add German language links to the translations page (#2495)

Author: jay-es

src/translations/index.md

@@ -25,6 +25,7 @@ aside: false
 - [العربية / アラビア語](https://ar.vuejs.org/) [[source](https://github.com/vuejs-translations/docs-ar)]
 
 - [Español / スペイン語](https://vue3-spanish-docs.netlify.app/) [[source](https://github.com/icarusgk/vuejs-spanish-docs)]
+- [Deutsch / ドイツ語](https://de-vue-docs.netlify.app/) [[source](https://github.com/vuejs-translations/docs-de)]
 
 ## 新しい翻訳の開始 {#starting-a-new-translation}