The language barrier does not excuse
I also wanted to write the same.
It is more than just a language barrier. Chinese people are very smart and most of them know English very well, especially written form of it (many of them have a hard accent, but the game is not this case - you have a written form, even have the translator that can be always and easily used in chat (it is not perfect, but enough to understand the idea).
This is something else, and neither racism as well. Because they don't "hate" foreigners. They just don't except them, distantly and indifferently. With no hate or negativity, just as the matter of fact.
I played so many mobile games and saw them dominating the top in all of them by their own groups, separate from each other.
Yes, they can win like this.
This is a nice tactics which gives better interaction between own trusted people.
But they live in the big World with many other people, and not letting them in simply takes away a big piece of life - possibilities and opportunities to know and learn other minds, logic, thoughts, attitudes etc.
We had and have a good group of people from S94 (old Culwood) with English-Russian-Spanish-French-Chinese-Vietnamese-Arabic speaking players in one house, and don't have any problems at all, and go fine with everyone. Because we TRY. And find ways to not forget someone behind.
If there are any issues - there always found the way to solve it.
I don't know why Chinese guys behave like that, but I would advise them to change the attitude and be more open to the World, they will never regret.