Even within nations, particularly multicultural nations, it’s common to have psychologists who specialise in specific cultures to provide the most appropriate advice. When I studied psychology in Uni we did a segment on psychological differences across cultures and they’re really quite stark. I don’t know enough about Japanese culture to be able to counsel a suicidal salaryman, but I can definitely help others who share my culture look after their mental health.
There are no known psychological truths across cultures. Because our culture heavily impacts our psychology, the two tend to covary. No one therapist can give quality advice to an Anglo farmer, a Sentinelese woman, a Siberian child and a Moroccan man. The cultural contexts just vary too wildly.