When trying to import new phrases, a Server Error is given instead. I already messaged the Curse Support, so far without much success.

This one is on Curse/WowAce, most likely. They should have created a ticket with the developers, but no one knows if and when they will fix the errors.

It may also be a permission issue, in which case they should still report back to let me know.

Turns out this is caused by attempting to import an empty string, which (for some reason) was added to the localization table in 2014: c3581ed

Still in contact with CF staff to see if this is on their end, but I'll remove it for the time being. It doesn't appear to be used anywhere.

Fixed in 425ab4b