Sure, things can go wrong with robots, but it’s rarely psychological.

One suggestion, send multiple identical ships, each crewed by members of each nation, where only one member of each crew would need to be fluent in the other’s language. This would be easier to arrange and would be more robust. Not only would the mission have a backup, even the loss of one bilingual crewman would still not cripple communications. Still, it might introduce other stresses and divisions it is difficult to anticipate. A lot can go wrong on a two or three year mission. The more complex you make it, the more things can fail, but the more redundancies you have available. A typical engineering challenge: how do you optimize the complexity to minimize failure?

The problem is similar to the classic one of choosing a crew size. Under the stresses of space, one guy might go crazy. Two might become enemies, with three, two might gang up on the third. We know large crews under strong hierarchichal chains of disciplined command seem to work, as in the military, but they sometimes fail too. But can you do this with two rival nations working together? No one has ever done this before, we just don’t know. The only comparable experience we have is submarine crews, but their cruises are much shorter than a Mars mission, the sailors aren’t prima donnas like astronauts, and they can be aborted at any time if necessary if there’s an emergency.

And the question arises, what if you have a disciplinary problem? Or sexual tensions and rivalries (there will certainly be women aboard). I recall reading about one simulated Mars mission where a male crewman sexually assaulted a female member. Space crews are no doubt exceptional people, and have undergone extensive vetting, but this is a very stressful environment where we have relatively little experience.

I don’t doubt this aspect has been studied in simulations, and on ISS missions, but very few results have been leaked to the public.