TheoTown

Is it possible to mod theotown with Java or do you need json for that? Also, is it possible to create menu items like the roads tab

Java? Nope, that's not how Google wants Android to work and I also would have some concerns if it would be possible.

Not yet, but I also think that it might be useful to create own categories...

Ok, thank you

I have to correct myself, it's possible to side load some code. However, it's still a security concern and I'm pretty sure that some virus scanners (like that one built into Play Store) might not like it.