feat(backend): Add language fallback for YouTube transcription block

[Copilot]

Problem

The YouTube transcription block would fail when attempting to transcribe videos that only had transcripts available in non-English languages. Even when usable transcripts existed in other languages, the block would raise a NoTranscriptFound error because it only requested English transcripts.

Example video that would fail: https://www.youtube.com/watch?v=3AMl5d2NKpQ (only has Hungarian transcripts)

Error message:

Could not retrieve a transcript for the video https://www.youtube.com/watch?v=3AMl5d2NKpQ! 
No transcripts were found for any of the requested language codes: ('en',)

For this video (3AMl5d2NKpQ) transcripts are available in the following languages:
(GENERATED) - hu ("Hungarian (auto-generated)")

Solution

Implemented intelligent language fallback in the TranscribeYoutubeVideoBlock.get_transcript() method:

1. First, tries to fetch English transcript (maintains backward compatibility)
2. If English unavailable, lists all available transcripts and selects the first one using this priority:
   • Manually created transcripts (any language)
   • Auto-generated transcripts (any language)
3. Only fails if no transcripts exist at all

Example behavior:

# Before: Video with only Hungarian transcript
get_transcript("3AMl5d2NKpQ")  # ❌ Raises NoTranscriptFound

# After: Video with only Hungarian transcript  
get_transcript("3AMl5d2NKpQ")  # ✅ Returns Hungarian transcript

Changes

• Modified backend/blocks/youtube.py: Added try-catch logic to fallback to any available language when English is not found
• Added test/blocks/test_youtube.py: Comprehensive test suite covering URL extraction, language fallback, transcript preferences, and error handling (7 tests)
• Updated docs/content/platform/blocks/youtube.md: Documented the language fallback behavior and transcript priority order

Testing

• ✅ All 7 new unit tests pass
• ✅ Block integration test passes
• ✅ Full test suite: 621 passed, 0 failed (no regressions)
• ✅ Code formatting and linting pass

Impact

This fix enables the YouTube transcription block to work with international content while maintaining full backward compatibility:

• ✅ Videos in any language can now be transcribed
• ✅ English is still preferred when available
• ✅ No breaking changes to existing functionality
• ✅ Graceful degradation to available languages

Fixes #10637
Fixes https://linear.app/autogpt/issue/OPEN-2626

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Original prompt

Issue Title: if theres only one lanague available for transcribe youtube return that langage not an error
Issue Description: Could not retrieve a transcript for the video https://www.youtube.com/watch?v=3AMl5d2NKpQ! This is most likely caused by: No transcripts were found for any of the requested language codes: ('en',) For this video (3AMl5d2NKpQ) transcripts are available in the following languages: (MANUALLY CREATED) None (GENERATED) - hu ("Hungarian (auto-generated)") (TRANSLATION LANGUAGES) None If you are sure that the described cause is not responsible for this error and that a transcript should be retrievable, please create an issue at https://github.com/jdepoix/youtube-transcript-api/issues. Please add which version of youtube_transcript_api you are using and provide the information needed to replicate the error. Also make sure that there are no open issues which already describe your problem! you can use this video to test: https://www.youtube.com/watch?v=3AMl5d2NKpQ`
Fixes https://linear.app/autogpt/issue/OPEN-2626/if-theres-only-one-lanague-available-for-transcribe-youtube-return

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Here's the code health analysis summary for commits 0fc6a44..81413ae. View details on DeepSource ↗.

Analysis Summary

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[AutoGPT-Agent]

Thank you for starting work on this YouTube transcription fallback feature! Since this is marked as WIP, I understand it's not ready for merging yet. Here's what needs to be addressed before this can be approved:

1. The PR title needs to follow the conventional commit format (e.g., fix(blocks): Add fallback for YouTube transcription when English is unavailable)

2. Once the implementation is complete, please make sure to:

   • Check off all items in your checklist
   • Provide a complete description of all changes made
   • Ensure your code changes align with the scope mentioned in the title

3. Consider adding more details about your implementation approach, especially how you plan to fallback to the first available language when English is not available

I look forward to reviewing this PR once the implementation is complete!

[AutoGPT-Agent]

Thanks for working on this YouTube transcript fallback feature! Your implementation looks technically sound with comprehensive test coverage. Before this PR can be merged, there are a few things to address:

1. The PR title needs to follow our conventional commit format. Since you're fixing an issue with YouTube transcription, something like fix(blocks): YouTube transcription fallback for non-English videos would be more appropriate.

2. The PR is marked as WIP and has an incomplete checklist item ("Manually verify the fix works as expected"). Please complete this verification step before requesting a review for merging.

3. Please convert your progress checklist to our standard PR template format, including the appropriate sections from the template. Since this is a code change, the code change checklist section would be required.

Once these items are addressed, the PR will be ready for a full review. The implementation itself looks promising - adding fallback to any available language when English transcripts aren't available is a good solution to the problem.

[AutoGPT-Agent]

Thanks for working on this YouTube transcription fallback feature! The implementation looks solid and includes comprehensive test coverage.

However, before this PR can be merged, a few items need to be addressed:

1. PR Title Format: Please update the title to follow our conventional commit format. Since this is fixing an issue with YouTube transcription, something like fix(blocks): Add fallback for non-English YouTube transcripts would be appropriate.

2. Complete the Checklist: The PR is marked as WIP with one remaining task: "Manually verify the fix works as expected". Please complete this verification using the example video from the issue (https://www.youtube.com/watch?v=3AMl5d2NKpQ).

3. Remove [WIP] from Title: Once the work is complete and you've verified the fix works as expected, remove the WIP marker from the title.

The implementation itself looks good - the fallback mechanism correctly tries English first, then falls back to other available transcripts with a preference for manually created ones over auto-generated. The test coverage is thorough, covering all the different scenarios including the fallback logic.

[AutoGPT-Agent]

Thanks for your PR implementing the YouTube transcription language fallback feature. The implementation looks solid, with comprehensive test coverage and good documentation updates.

Before we can merge this PR, please update the title to follow our conventional commit format. It should be structured like: fix(blocks): Add language fallback for YouTube transcription to clearly indicate the type of change and affected component.

Your implementation looks good - I particularly appreciate how you've:

• Added fallback logic that maintains priority for manual transcripts
• Created comprehensive test coverage for the new functionality
• Updated the documentation to reflect the new behavior

Once the title is updated from the current WIP format to the conventional commit format, this should be ready for final review.

[AutoGPT-Agent]

Thank you for your work on implementing the YouTube transcription fallback feature. The implementation looks solid with good test coverage and documentation updates.

Before we can merge this PR:

1. Please update the PR title to follow our conventional commit format. For this change, something like fix: YouTube transcript fallback to non-English languages would be appropriate.

2. Your PR is marked as [WIP] - is this ready for review and merging now? If yes, please remove the WIP tag.

3. For future PRs, please use our standard PR template format with the checklist. While your current format has good information, consistency helps reviewers.

The technical implementation looks excellent - the fallback logic is well-designed, thoroughly tested, and properly documented. Nice work on the comprehensive test suite!

[AutoGPT-Agent]

Thank you for your detailed PR implementing YouTube transcription language fallback. The code changes look well-implemented with comprehensive testing and documentation updates.

Before this can be merged, there are two issues that need to be addressed:

1. PR Title Format: Your current title "[WIP] Copilot Request" doesn't follow our required conventional commit format. Please update it to something like:
   fix(platform/blocks): Add YouTube transcript language fallback

   Also, the [WIP] tag suggests this is still a work in progress, but your description indicates it's complete and ready for review.

2. Missing Standard Checklist: While you've provided excellent custom information about your changes, we require the standard PR checklist to be included and completed. Please update your PR description to include the standard checklist from the template.

Your implementation looks solid - the code changes are focused, well-tested, and include appropriate documentation updates. Once you address these formatting issues, this PR should be ready for final review and merge.

[qodo-merge-pro]

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 2 🔵🔵⚪⚪⚪

🧪 PR contains tests

🔒 No security concerns identified

⚡ Recommended focus areas for review API Usage The code accesses private attributes (_manually_created_transcripts, _generated_transcripts) of TranscriptList. This may break with library updates; consider using public APIs if available or add guardrails. available_transcripts = list( transcript_list._manually_created_transcripts.values() ) + list(transcript_list._generated_transcripts.values()) Error Context When falling back fails due to empty lists, the original NoTranscriptFound is re-raised without additional context. Consider logging available languages or lack thereof before raising to aid debugging. if available_transcripts: # Fetch the first available transcript return available_transcripts[0].fetch() # If no transcripts at all, re-raise the original error raise