Add comments to Greeter's po files to explain how accelerators works
In some languages, they have problems with Greeter’s accelerators: they are removed or the same letter is use twice.
Adding comments for all accelerators in po files could avoid (at least few) of theses mistakes.
Related issues
- Related to #13635 (closed)
- Related to #15619
Original created by @xin on 14457 (Redmine)