Feature request: Auto-detect user locale for currency display in terminal

Feature Request

Problem

When Claude Code displays monetary values in the terminal (e.g. extra usage credits, cost tracking), it shows a USD currency symbol regardless of the user's location. Users in different regions see an unfamiliar currency format — for example, a user in the UK sees $ instead of £, or a user in Europe sees $ instead of €.

Proposed Solution

Claude Code could detect the user's locale/region and automatically display the correct currency symbol when showing monetary amounts in the terminal. This could be done by:

1. Reading the system locale — Intl.DateTimeFormat().resolvedOptions().locale in Node.js, or environment variables like LANG, LC_MONETARY, or LC_ALL
2. Mapping locale to currency — e.g. en-GB → £, de-DE → €, ja-JP → ¥, en-US → $
3. Applying the symbol wherever currency values are rendered in the terminal output (usage summaries, cost displays, etc.)

A manual override in settings (e.g. "currency": "£") would also be useful for users whose system locale doesn't match their preferred currency.

Additional Context

Claude Code has a large international user base. Auto-detecting currency would be a small quality-of-life improvement that makes the tool feel more polished and localised out of the box.