Add check functionality to check if translated po files in PRs have are based on the current source version

[ReadyPlayerEmma]

The goal would be to prevent merges of new translations based on outdated source files.

Just comparing the source header fields should be sufficient, but more advanced approaches would be welcome too.

[ReadyPlayerEmma]

@fangfufu or @Tar-Minyatur would either of you be willing to look into adding this?