(Please include your Gramps version and Operating System)
made a custom filter on ‘Kaste’
When clicking ok it automagically changed spelling ‘Caste’
AIO64-6.0.8–1
So, in the Dutch, you selected from the translated terms in the built-in “Attributes” pop-up list and the Rule Editor showed the untranslated term.
This would seem to be an “enhancement” that needs to be requested, not a bug report. The translation is not “broken”, it is not yet implemented for the “Personal Attribute”. (And potentially, for all rules using a menu combo box.)
FYI, there is a prototype for Gramps 6.2 that would allow you to change the translation on your computer, and then to submit it for others to use as well.
The Pig Latin translation overlay would only reveal this particular problem once a Selector combo box menu item had been selected.
How can a menu selection be included in the tests for translation completeness?