"Chinese women are very beautiful."
Translation:Çinli kadınlar çok güzeller!
The ending -ler is actually a copula ending not a plural ending in this sentence. It means (they) are. Like the Spanish son. But you don't have to use it when there is a subject which is already plural. Therefore Çinli kadınlar çok güzel. is also correct.
If there were no subject it would be mandatory because you need to know that you are talking about more than one person. e.g. Çok güzeller. -> They are beautiful. and Çok güzel. -> He/she/it is beautiful.