Need best way to find mental doc to work with different language and literacy issue?

Doctors rely on more than conversation, they look at the whole patient, how they walk, how they talk, how they move. Do they know what day it is? Can they draw a clock? Can they remember three things? Can they count backwards? You can do the tests yourself with her.
Bloodwork will tell the MD how well kidneys and liver are working, not what the patient says. Please try to accept what they tell you.

Another thought - research to find psychiatric and neurology associations of doctors; these professional groups have members in that profession and might have information on who speaks different languages.

Call the local hospitals to see if they have referral services for doctors, and ask if any speak your mother's native language. The hospital we go to lists the doctors, their professions, and which languages they speak. It would be easier if I could just search their website by language spoken, but it's not set up that way. However, other hospitals in other areas might have more sophisticated methods of finding doctors proficient in other languages.

This is just a guess but is there an association of people of her nationality? If so, perhaps you could contact them and ask if they know of any doctors who speak her language. If there are enough people for a group to be affiliated, then they must have some doctors, and perhaps some know of doctors who could communicate with your mother in her native language.

You write that she expresses a death wish; so I assume you understand what she's saying in her own language? Couldn't you interpret for the doctors?