if you do something like
{$foo='test"123'} {translate text=$foo}
so it results with a quotation mark in the string, it isn't escaped when
generating the translations.dat file. This results in it being corrupted and the
offending items can't be deleted.

Workaround was to remove the strings, then edit the translations.dat file making
sure to keep the string lengths the same (changing " to x for example), then
deleting them from the interface. There is perhaps an easier way but this did
the job.