Add `mtt_check.py` from Minetest Translation Tools

A while ago, I also wrote a `.tr` file checker to check for syntax errors, called `mtt_check.py`. You can find it here:

https://codeberg.org/Wuzzy/Minetest_Translation_Tools

Please tell me what you think about it and if it's good enough for inclusion and if not, what needs to be changed.

Start by reviewing the linked Minetest Translation Tools project and its mtt_check.py implementation, then compare it with this repository's existing tooling conventions. Determine whether the .tr syntax checker is suitable for inclusion and document any changes needed before it can be accepted.

Written by the indexing model from the issue text.