Topics API now accepts lang= parameter. When lang=de, the word
labels are translated from English via Kaikki translations:
"eye, pupil, iris" → "Auge, Pupille, Iris"
Frontend sends searchLang to /topics endpoint and displays
display_words (translated) instead of words (English).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>