[translate] Fix zh-CN lang code

[atuchin-m]

Resolves brave/brave-browser#25417

This PR changes the default in the code.
The older browser versions also will receive the new list via Griffin: brave/brave-variations#366.
But the default list is still used for restored pages (a Chromium thing, the startup pages usually load faster than the language list request).

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally: npm run test -- brave_browser_tests, npm run test -- brave_unit_tests, npm run lint, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

[atuchin-m]

a weigh formatting for clang-format.
BTW we will soon delete this file (after enabling the all languages)

[iefremov]

don't we have tests?

[atuchin-m]

don't we have tests?
@iefremov it's mostly hardcoded data than a code/state machine that could be tested.
We could write a test that kBraveDefaultLanguageList is actually used, but this src override was designed as temporary (until we support all the Chromium languages).

[linhkikuchi]

can we also add "zh-TW" to default list?

[atuchin-m]

@linhkikuchi
Hm, I can't see that it's supported on https://translate.brave.com/translate_a/l