自助餐 (zi4zhu4can1), literally “self service meal,” is the Chinese word for buffet. Buffets in China are universally found in 5-star hotels and are similar to how we treat buffets in the US. Among the specialty restaurants that provide unlimited food, they adopt a number of limitations to make sure that they still turn a profit. For example, time limits are generally imposed (typically in the range of 90 to 120 minutes) and complex rule systems penalizing wasted food. The best items are nearly inaccessible behind a long queue where the food is either only served for brief intervals or limited to one portion per person.
Buffets in Taiwan, specifically the vegetarian buffets, are a different beast altogether. One fills up a plate as one wishes, but pays according to the total weight of the food. That also happens to be how 串串香 (chuan1chuan1xiang1, a type of Sichuan hotpot with skewers) is calculated, where it is easier to weigh the pile of skewers than count them.
While on the topic of unlimited food, free refills is 续杯 (xu4bei1, literally “supply more cup”), while if one is getting unlimited alcohol as part of a meal special or happy hour, the term is 畅饮 (chang4yin3, literally “free drinks” meaning “to drink one’s fill”).
Finally, the Korean for all-you-can-eat is 무한리필 (muhan ripil) which combines Chinese with English. Muhan based on 无限 (wu2xian2, “unlimited”), while ripil is a sound loan of “refill.”