When you ask an AI agent something in Korean or Spanish, does it search in that language? I ran 320 web-search sessions with Claude Code (Opus 5.5) and Codex CLI to find out.
Global topic (AI products), asked in Korean, Japanese, Spanish or Ukrainian:
Local topic (metro fare, this week's news, restaurants in Seoul, Tokyo, Madrid, Kyiv), 5 runs per question:
| Claude Code | Codex | |
|---|---|---|
| Asked in the local language: searches in that language | 82% | 50% |
| Asked in English: searches in the local language | 49% | 17% |
Why it matters: if you publish in a language other than English, AI agents may only find you for local topics. For global topics, the English web wins.
Every query, cited URL and the language of each cited page are in the dataset (CSV/JSON, CC BY 4.0): https://tokensave.app/data/claude-web-search-by-language
source & further reading
dev.to — original article
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