It is quick hard to know how to change language setting on Android which require multiple steps to open the language setting and do the switch.

This app helps open language setting instantly without tapping multiple times.

Design for people who needs to switch languages often.

Amazon Fire Tablet user would find this particular useful.

If your language is not available for switching please check your device supported language with the following app
https://play.google.com/store/apps/details?id=name.ratson.dlangs