Is it permissible to participate in collective remembrance (dhikr) and supplication (du'a) after prayer, or to continue praying behind someone who makes errors in recitation, or to pray in congregation at home, or to pray behind someone who makes errors in the silent prayers, given the presence of innovations (bid'ah) and problems in the imamate at a mosque frequented by non-Arab Muslims?

It is obligatory to follow the Sunnah and avoid the people of innovation. It is not permissible to participate with the people of innovation in their innovations. Whoever pleases people by displeasing Allah, Allah entrusts him to the people. Some reading errors invalidate the prayer, and there is no difference between audible and silent prayers in this regard. It is not obligatory to pray in that mosque; one can move to another mosque or pray in congregation in homes if no other mosque is available.