There are two documents you should read:
http://dev.minetest.net/Androidhttps://github.com/minetest/minetest/bl ... ME.androidPlease note that minetest is LGPL licensed, and you have to abide its terms.
Specifically, you'll need to make the engine (if you do any modifications) LGPL or GPL licensed as well, best to publish it on github or so. The LGPL license has been chosen so that mods can be proprietary, if the people developing them chose so.
If you decide to enable network connectivity and sync with our public server list, be so nice and update to the latest copy of our source from time to time (perhaps every stable release or so), as we have many minetest based apps in the play store with very outdated versions of minetest, hindering evolvement of the protocol, and leaving the users with age old bugs that are long fixed by us, just the app publisher didn't update their build.