What is the law regarding working Christmas Day in China? Do companies that employ foreigners have to respect their employees’ cultural festivals or is it just another workday?
There is no widespread law about this. Christmas and other foreign holidays given to employees depends on what their work contract states. One thing to keep in mind is that this part of the contract is usually negotiable.
If you feel strongly about this point or the holiday is especially significant to you, let your employer know before signing a new contract. They could very well amend this part to suit your cultural traditions.