I don't know much about PPA's. I would expect them to put everything on the right place. It is possible that inside your main minetest folder there's a a folder called "minetest_game-
some serial number". If you find this one, move it to the folder "games" (minimal should be present in it). Then rename the "minetest_game-
some serial number" to "minetest_game". It might even work! I never had to try this out.
My personal favourite is to 'compile' the latest version. I exactly follow (copy the lines after $ and paste them in my terminal) the instructions under the readme.txt, under "Compiling on GNU/Linux:". You can find those here
https://github.com/celeron55/minetest (you need to scroll down around 1/3 page.
- To get the dependencies you must put "sudo" before the line(s). Probably you already got the latest through the PPA
- cd celeron55-minetest-286edd4 (or similar) --> It's now "cd celeron55-minetest--25cf375 (you can open your file manager to see which number you need)
- To run minetest I use the file manager, so I exit after finishing make -j2 (2 can be higher if you have more than 1 core, so it goes faster, I use 2 for my dual core, because I never noticed much difference and it works).
Good luck!