Multi-language support optimization

[ONDAAA]

Model is already multilingual (paraphrase-multilingual-MiniLM-L12-v2) but:

• Test accuracy on non-English comments (CZ, DE, ES, JP, etc.)
• Calibrate confidence thresholds per language
• Localize UI strings (popup, overlay text)
• Handle mixed-language videos (EN subtitles, non-EN comments)