I would just start with the COOL language.
it's a stanford default language for students to program.
You should just start with those videos and you can see a multitude of cool compilers online.
there is also the:
nand2tetris.org project which lets you build the electrics etc first before going into the language design... but that's maybe overkill.
If you're in a country where you get free university access (like I do) you could also look up compiler / language design and just participate in the university.