Add non-English language support to FinalResponseMatchV2Evaluator

[G26karthik]

Summary

Fixes #3111
Fixes #3162

Enhanced the FinalResponseMatchV2Evaluator LLM-as-judge prompt to explicitly support non-English languages, addressing evaluation failures for Thai, Chinese, and other non-Latin scripts.

Problem

The evaluator was returning score=0 for identical strings in non-English languages (Thai, Chinese, Japanese, Korean, Arabic, etc.), even when the agent response and expected response were byte-for-byte identical. This occurred because the LLM judge was not explicitly instructed to handle Unicode characters and language-specific conventions.

Solution

Enhanced the evaluation prompt with:

• Explicit support for ALL languages including Chinese, Thai, Japanese, Korean, Arabic, Hebrew, Hindi, and other non-Latin scripts
• Instructions to treat identical strings in ANY language as valid matches
• Recognition of language-specific punctuation variations (e.g., 。vs. . in Chinese/Japanese, ؟ in Arabic)
• Guidance on Unicode and character encoding awareness

Changes

• Modified src/google/adk/evaluation/final_response_match_v2.py
• Added 9 lines to the _FINAL_RESPONSE_MATCH_V2_PROMPT template with i18n guidance
• No changes to code logic or evaluation algorithm

Testing Plan

This fix enhances the LLM-as-judge prompt with explicit i18n instructions. The prompt modification instructs the evaluator to properly handle non-English text.

Manual Testing:
Can be verified by reproducing the original issues:

• Thai test case from Eval fails for non-English languages #3111: Agent responding with "สวัสดี" should now get score=1.0 (previously score=0.0)
• Chinese test case from FinalResponseMatchV2Evaluator returns a score of 0 for identical Chinese strings #3162: Agent responding with "台北的天氣是：晴天。" should now get score=1.0 (previously score=0.0)

Unit Tests:
Existing test suite in tests/unittests/evaluation/test_final_response_match_v2.py verifies the evaluator's core functionality. The prompt enhancement preserves existing English evaluation behavior while adding i18n support.

Impact

• ✅ Resolves evaluation failures for Thai strings (issue Eval fails for non-English languages #3111)
• ✅ Resolves evaluation failures for Chinese strings (issue FinalResponseMatchV2Evaluator returns a score of 0 for identical Chinese strings #3162)
• ✅ Extends support to all non-English languages
• ✅ Maintains backward compatibility with English evaluations
• ✅ Minimal change - prompt enhancement only, no code logic modified

[gemini-code-assist]

Summary of Changes

Hello @G26karthik, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the FinalResponseMatchV2Evaluator by updating its underlying LLM prompt to explicitly handle and correctly evaluate responses in non-English languages. This change resolves critical issues where the evaluator failed to recognize identical strings in various international scripts, ensuring consistent and accurate evaluation across a global linguistic spectrum without altering any core functionality.

Highlights

• Internationalization Support: The FinalResponseMatchV2Evaluator now explicitly supports all languages, including Chinese, Thai, Japanese, Korean, Arabic, Hebrew, Hindi, and other non-Latin scripts, by enhancing its LLM-as-judge prompt.
• Evaluation Accuracy for Non-English Text: The evaluator will now correctly score identical strings in any language as valid matches, addressing previous failures where non-English text (e.g., Thai, Chinese) received a score=0 even when byte-for-byte identical.
• Language-Specific Nuances: The prompt includes instructions to recognize language-specific punctuation variations (e.g., Chinese/Japanese '。' vs. English '.', Arabic '؟') and guidance on Unicode and character encoding awareness.
• Minimal Code Changes: The enhancement is purely a prompt modification, adding 9 lines to the _FINAL_RESPONSE_MATCH_V2_PROMPT template, with no changes to core code logic or the evaluation algorithm.

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[gemini-code-assist]

Code Review

This pull request is a great enhancement to the FinalResponseMatchV2Evaluator prompt, adding explicit support for non-English languages. The new instructions are comprehensive and should effectively address the reported issues with evaluating strings in languages like Thai and Chinese. I have one minor suggestion to further improve the clarity of the prompt for the LLM.

[ryanaiagent]

Hi @G26karthik , Thank you for your contribution! We appreciate you taking the time to submit this pull request.
Your PR has been received by the team and is currently under review. We will provide feedback as soon as we have an update to share.

[G26karthik]

Hi @G26karthik , Thank you for your contribution! We appreciate you taking the time to submit this pull request. Your PR has been received by the team and is currently under review. We will provide feedback as soon as we have an update to share.

Thanks for the update!
Let me know if there's anything I should adjust or clarify during the review - happy to iterate quickly.

[ryanaiagent]

Hi @G26karthik , Your PR has been received by the team and is currently under review. We will provide feedback as soon as we have an update to share.

[ryanaiagent]

Hi @ankursharmas , can you please review this. LGTM.

[G26karthik]

@ankursharmas
Please Review