Is it permissible to work in a company that has a Christian foreign partner, taking into account the possibility that the source of his capital is unlawful (such as gambling or alcohol production), and does this affect the permissibility of working and earning in this company, most of whose partners are Muslims?

There is no harm in a Muslim partnering with a non-Muslim in a company that is permissible according to Sharia, even if the non-Muslim's capital comes from an illicit transaction like usury. The sin of that lies with the earner, not with the one who deals with him through permissible means. The Prophet, peace and blessings be upon him, dealt with the Jews, who consumed usury and illicit gain. He bought from them and ate from their food, which indicates the permissibility of dealing with someone whose earnings are impure, without that being forbidden for anyone other than the earner.