Fix: DeepL translation doesn't work for Simplified Chinese

[mshibanami]

(No related issue)

Problem

Suppose you want to translate an English word "Hello" to Simplified Chinese with DeepL API via BartyCrouch.
Currently, BartyCrouch sends a request like this:

https://api-free.deepl.com/v2/translate?source_lang=En&text=Hello&target_lang=Zh-Hans&auth_key={auth key}

But DeepL doesn't allow Zh-Hans for target_lang nor source_lang, so they always return 400 Bad Request.

This is the documentation of what they allow: https://www.deepl.com/docs-api/translating-text/request/

Proposed Changes

• Set ZH rather than Zh-Hans for target_lang and source_lang
  • I didn't do this for Traditional Chinese because DeepL's ZH is actually for Simplified Chinese but I have no strong opinion. Please feel free to suggest me doing this for Traditional Chinese too.
• Change the values of target_lang and source_lang to UPPER CASE from Capitalised Case
  • This is a kind of refactoring. As of now, both uppercased and capitalized work fine, but I guess we better to use the documented case.

So this PR will change the above URL into this:

https://api-free.deepl.com/v2/translate?source_lang=EN&text=Hello&target_lang=ZH&auth_key={your auth key}

[Jeehut]

Thank you, code looks good to me. Merging! 🎉

[mshibanami]

Thanks!

[Jeehut]

Released in version 4.7.1. 🚀