Where does “katarietis” come from?

katarietis (Latvian) comes from Latvian -ietis — Added to nouns and adjectives to form masculine (-nieks) or feminine (-niece) nouns referring to people having the properties of the original noun, or living in the place designated by the original noun.

katarietis (Latvian): a Qatari man, a man from Qatar or of Qatari...