how does i write a hex editor?

I want to writer an exe trainer for a game that hex edits another program (the game) to hack it/train it.

I know what addresses to edit and stuff, but I need to know what language would be best to write it in.

Any idea?

This is the sort of thing that Malbolge is designed for. Write yourself an interpreter for malbolge. http://www.antwon.com/other/malbolge/malbolge.txt