The `UCKeyTranslate` function was being used wrong.
The `deadKeyState` param should use `kUCKeyTranslateNoDeadKeysMask`
instead of `kUCKeyTranslateNoDeadKeysBit` (optionally could also use
`(1 << kUCKeyTranslateNoDeadKeysBit`)).
This commit also dispenses with accessing the keyAction, as this is not
crucial for determining the key.
Comments have also been added to better describe the code.
Pull Request: https://projects.blender.org/blender/blender/pulls/109987
75658109be