Is MSE an appropriate place to post questions about translations/localization issues for mod related features?
If not, where should I do that?
Yes, in general, Meta.SE is an appropriate place to post bug reports, feature requests, and discussions about moderator tools. Localization is on-topic as well, as you're well familiar with :)
The exception is when the post would be about tools that are not public knowledge. Posts about those, including about localization, do not belong on Meta.SE, and instead should be directed towards the private Stack Moderators Team.
This generally includes tools such as those used to detect sockpuppets and voting fraud. If in doubt about whether or not the tool is public knowledge, err on the side of caution and use the Team; staff monitors posts there (especially if you use the needs-staff tag). You can also ask in the TL about specific tools before posting anywhere.