I used AndroidXmlSorter plugin and it works perfectly for me.
How to install:
Go to Android Studio -> Preferences -> Plugins and hit Browse repositories..
Search for AndroidXmlSorter, install and restart your Android Studio. Go to your strings.xml file and hit Ctrl+L. Voila.
Disclaimer: I’m not the author of this plugin, I just found it by chance and I think all the credits should go to the plugin author. The repo is here: https://github.com/roana0229/android-xml-sorter