Ethnic and more rare instruments are still pretty popular in film/game/trailer music and are of course a great tool to locate a scene or character or to simply add unusual textures. However these instruments pretty often come with technical limitations which make it trickier to use them. Sometimes they’re just limited to a specific set of keys or use a tone system that doesn’t fit that well on the western tempered scale. Additionally there might be some idiomatic standard phrases that are commonly played on them etc. Another problem is that musicians who can play these rare instruments might not be able to read western notation.
So when you’re planning on using such an instrument, do a good research on it and find a player before you start writing to talk about do’s and don’ts. A pretty common way of working with such instruments is to record everything else first and then do a solo session with the musician and let him/her improvise with a few instructions of what you want instead of writing out specific parts and possibly write something very unidiomatic and then later on compile a version of takes that you liked.
By that you will probably get the most authentic sound out of the instrument instead of trying to figure out how to notate certain things and still not getting the desired effect.