Add zh_CN messages resource

[ylk2534246654]

Add zh_CN messages resource

[rbri]

Thanks for the contribution.
I think we have some unit tests for the error message translation. Maybe you can enhance some tests.

[gbrail]

This is awesome work and it'll be great to have. Before merge, do you think that we could have:

1. A basic unit test that verifies that, when the locale is set, messages at least come out from the right catalog. "MessageProviderLanguageTest.java" does this -- we just need to update it for Chinese.
2. I'd like one other Chinese speaker to verify that these messages are indeed reasonable Chinese translations and are OK to add in the source code.

I can do #1 if there is someone in the community who can do the second part!

[p-bakker]

@gbrail I've pasted the content of the modified file with the Chinese translations into Google Translate and the translations seem to hold up just fine