Single Link field dropdown (references) do not show localized values

@technology, sorry I missed this earlier!

I’m afraid this isn’t functionality we currently offer, but there is a feature request for it here that you can vote on: Add locale validation to link field

In the meantime, as a workaround, might it help to manually label your titles (like [DE] test-at-only)? I know it’s clunky, and I agree that a proper solution (filtering by the same locale) would be useful.