Is it permissible to pay a bribe to non-Muslim tax officials to reduce taxes imposed unjustly, given that the questioner is from a Muslim minority in China?

Paying illegitimate taxes is an injustice, and repelling or alleviating injustice is religiously مطلوب (required). Therefore, there is no impediment to paying money to someone who can remove or alleviate this injustice. This is not a bribe, because a bribe is giving money to invalidate a right or validate a falsehood, and it is forbidden, as narrated by Abu Hurayrah (may Allah be pleased with him): "The Messenger of Allah (peace and blessings be upon him) cursed the briber and the bribed." This money is only paid to repel injustice, so there is no harm in that.