For Chinese, it’s usually a price per character. Many words include multiple characters in Chinese, but automatic word count in Chinese text is impossible because the same character is used in many combinations, creating different words. A Chinese text can combine a significant volume of information using very few words, and therefore the translation of this text becomes bigger.
Usually, a 1000 word English text translated into Chinese might be around 1300-1700 characters long, and vice-versa. Sometimes translator uses a multiplier of 1.5, i.e., 1500 Chinese characters, usually translates into about 1000 English words.