for android project you can access the absolute location using android.srouceSets.main.res.srcDirs[0].
In your plugin if i use this dir (absolute path) extra invalid dirs will be created.
I think it's better to access the project soucrce sets and use that dir' i can give you a "map" of poeditor langs to android langcodes so actually all that needs to be specified is the lang itself that you want to use.