It doesn't make sense to them to cut themselves off from the English-based open-source ecosystem just so they can use their native language when they already know enough English to get by.
Many programming languages already support Unicode identifiers and nativist movements exist (e.g. [0]), some people produce interesting mixed-language programs (e.g. stdlib in English, other identifiers in Chinese with Latin prefixes to indicate type: [1]) but it's overall a very small niche, because most people can see the value of being able to share code globally, which means using English.
[0] https://github.com/program-in-chinese/overview/
[1] https://github.com/cflw/cflw_py/blob/master/%E7%A8%8B%E5%BA%...