[style](index) Translate SNII comments and test diagnostics to English

[airborne12]

What problem does this PR solve?

Related PR: #67537

Problem Summary:

The SNII code and tests touched by #67537 contain Chinese comments and golden-corpus diagnostics. Translate that explanatory text to English, including the related FE policy and protobuf comments. Preserve all Unicode test inputs, executable logic, query expectations, and the on-disk format.

Also clarify two comments against the existing behavior: the control-byte sample is not the full internal marker, and missing golden expectations fail verification.

Release note

None

Check List (For Author)

• Test
  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

Validation:

• Tokenized C++/Java/Protobuf comparison of all 51 changed files: executable tokens are unchanged except seven translated test diagnostics; Unicode input data is preserved.

• Source scan: no Chinese comments remain in the changed files.

• Full merged-tree C++ clang-format 16 check passed across BE and Cloud sources/tests.

• Full merged-tree FE mvn clean checkstyle:check passed with JDK 17 and zero violations.

• bash build-support/check-build-hygiene.sh and git diff --check passed.

• No database build, unit-test execution, or regression cluster was needed for these comment/diagnostic-only edits.

• Behavior changed:

  • No. Only comments and test diagnostic wording change.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

Thank you for your contribution to Apache Doris.
Don't know what should be done next? See How to process your PR.

Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[airborne12]

run buildall

[hello-stephen]

Cloud UT Coverage Report

Increment line coverage 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	77.53% (2056/2652)
Line Coverage	65.74% (37608/57205)
Region Coverage	52.98% (35064/66180)
Branch Coverage	56.45% (11267/19958)