What is translate plugin? And how can I get one?

Translate plugin helps us to translate string resources inside an apk. APK Editor itself does not provide translate plugin, but provides interfaces for others to develop such plugins. Here is an exmpale: https://github.com/heagoo/apkeditor_plugin_translation. The exmpale demostrates how to do auto translation based on online translator.
To launch the plugin, please click the translate icon:

I successfully modified the apk, but it does not work. Why?

It may be caused by the bug of APK Editor, as you know, reverse engineering is always challenging and no solution can 100% work. And, the app itself may also be protected by the developer to prevent modifications.

Mofified apps can not show Google maps. Why?

As the apk is re-signed, you need to use your own Google Maps API key to make it work.

I cannot find the string which displayed inside the app, why?

Various reasons: like inside the smali code, dynamically generated, or even be encrypted.

Where can I learn more?

I am not a good teacher, please learn more from Google or youtube.