Add zh-CN translation

[bitaller]

I have created zh-CN translation resource. Please review it.

[fernandreu]

Wow, that was quick, thanks a lot! The format of the file looks fine (I'll trust you with the content itself 😅), so I'll merge it. The checks failed just because I hadn't updated the copyright year to 2021 yet, but it will be fine by the time this gets merged.

If you couldn't see the language menu, it might be because you are using one of the release versions; I only started working with the translations after the last one.

What I'll do next is:

• Add this language to that dropdown list
• Add your name to the About dialog / README page here (I'll put bitaller unless you have any other preference)
• Create a new development build and let you know, in case you want to do any more checks

If that goes well, I'll create an official Release 1.8 containing this translation.

Thanks again!

[bitaller]

It sounds great!