Obviously if you ignore the test results then the test doesn't make any difference. But if you assign some weight to whether their solution to a test problem worked (which is culture-independent, or at least less culture-dependent) rather than how well they explained themselves to a person from a particular culture (which is easier for people from that same culture), then you end up with a process that is much fairer across cultures. And similarly for non-culture aspects of a person's background.
If you can't explain yourself then I don't want to hire you. Developers are not sitting in a dark corner not interacting with anyone; they are working with the team, they are gathering requirements from end users, etc.
If you can pass a coding test but you can't express yourself in a way that anyone can understand, then that's a no-hire. If that's a cultural bias, so be it. I don't see how it can be any other way.
Now it's been my personal experience that culture doesn't matter too much. For more than half the team, English is a second language. HR will reject candidates for language reasons even before I get to them.
