Add "msgfmt --check-accelerators" to quality checks

[luebbe]

Gettext msgfmt offers the --check-accelerators option to check if both, msgid and msgstr have an accelerator key.

It would be nice to have this available as an additional quality check in Weblate.

[luebbe]

If I wanted to tackle this task, where should it belong? An additional class in checks/consistency.py would come to mind.

[nijel]

You can create new file for that, that's probably best approach.