Feature: /insights should respect user's language preference

Summary

The /insights command always generates reports in English, ignoring the user's language preference set in CLAUDE.md (e.g., 默认使用中文回复). Users who work in non-English languages have to spend extra tokens asking Claude to translate the entire report afterward, which is wasteful and redundant.

Current Behavior

• /insights always outputs the report in English (both the terminal summary and the HTML report)
• Even with CLAUDE.md specifying a default language, the report language is hardcoded
• Users must manually ask Claude to translate the output, wasting tokens and time

Expected Behavior

/insights should respect the user's language preference. Possible approaches:

1. Flag-based: /insights --lang zh or /insights --lang ja
2. Auto-detect from CLAUDE.md: Read the user's language preference from their CLAUDE.md instructions
3. Config-based: Add a language field in .claude/settings.json

Any of these would work — the key is that non-English users shouldn't have to pay the token cost of translating a full report every time.

Context

As a Chinese-speaking researcher, I run /insights regularly to review my usage patterns. Every time I have to ask Claude to re-render the entire report in Chinese, which:

• Wastes tokens (the report is lengthy)
• Adds an extra round-trip
• Feels like an obvious gap since CLAUDE.md already supports language preferences

Environment

• Claude Code CLI
• macOS