Squash commits only if author + language match

### Describe the problem

Currently, it is possible to set up squashing by author, language, or all into one.
All of these have issues:

1. Author: says "Translated using Weblate to " but commit may contain many other languages
2. Language: the least worst, but mixes potentially harmful contributions with valid contributions in a single commit, loses authorship
3. Into one commit: Just everything specific is lost in the end.

### Describe the solution you would like

Instead of squashing based only on those properties specifically, squash based on the author and the language. That way, contributions to multiple files are squashed into one, quick changes in other commits are squashed, but authorship isn't lost, and it becomes easier to find issues.

### Describe alternatives you have considered

I can't think of much else, I like this approach, microG seems to do this manually which I found very nice

### Screenshots

_No response_

### Additional context

_No response_