At the moment, the Marriage Law of the People's Republic of China adopted on September 10, 1980, defines marriage as a union between a man and a woman. However, late last year, China's top legislative body has been advised to legalize same-sex marriage in the updated civil code.
According to a Bloomberg article:
The Commission for Legislative Affairs of the National People’s Congress Standing Committee has received more than 237,000 online suggestions and 5,600 letters requesting to clarify the “scope of close relatives, improving the common debt of spouses and legalizing same-sex marriage,” according to the report, which cited Yue Zhongming, spokesman of the commission.
The report didn’t specify if the legislature will include the legalization of same-sex marriage in the civil code. The NPC will review the draft of the new civil code in March 2020, according to its website.
The question asks: When will China legalise same-sex marriage?
The question takes "legalisation" to mean an amendment of the Marriage Law of the People's Republic of China, widening the legal definition of marriage to encompass same-sex couples. It resolves on the date that such legislation is passed by the National People's Congress, and resolves ambiguously should the People's Republic of China cease to exist in one form or another.
This question resolves as "> Jan 1, 2100" if it does not resolve positively or ambiguously before 01/01/2100.