What is the ruling on washing clothes in non-Muslim countries if they are mixed with the clothes of non-Muslims, and what is the solution for dealing with old clothes that were washed in this manner?

There is no impediment to washing the clothes of a Muslim with the clothes of disbelievers. However, if their clothes are inner garments and have touched their private parts, it is preferable not to wash them with the clothes of a Muslim, due to the possibility of them being defiled, as many of them do not guard against impurity. It is possible to request that the Muslim's clothes be washed separately if feasible. What has been previously washed is not to be judged as impure, because the impurity of their clothes is not certain. Many scholars are of the opinion that the clothes of disbelievers are pure and permissible to use unless their impurity is known.