[FEATURE] Permission prompt explanation (Ctrl+E) should respect language setting

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The permission prompt's "explanation" text (toggled via Ctrl+E) appears to be generated by a small LLM (likely Haiku-class), but it always responds in English regardless of the user's language setting configured via /config.

This is fundamentally different from the static UI localization issue tracked in #4866 (which covers hardcoded CLI strings like "Allow/Deny"). Since the explanation text is LLM-generated, it should be straightforward to pass the user's language preference to the model and generate the response in that language — no i18n framework or translation files needed.

Issue #23592 was closed as a duplicate of #4866, but it conflated two distinct problems:

1. Static UI localization (button labels, status messages) — requires i18n infrastructure (#4866)
2. LLM-generated explanation text — only requires passing the language setting to the model prompt

This issue specifically addresses problem (2).

Proposed Solution

When generating the permission explanation text (Ctrl+E), include the user's configured language (from /config → Set Language) in the prompt to the explanation model, so the response is generated in the user's preferred language.

Alternative Solutions

• Users can read the English explanation and mentally translate, but this defeats the purpose of the language setting.
• The current workaround is to just accept/deny without understanding the explanation.

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

Use Case Example

1. User sets language to 日本語 via /config
2. Claude generates a Bash command like find /path | xargs rm
3. Permission prompt appears; user presses Ctrl+E to understand what the command does
4. Currently: explanation is in English
5. Expected: explanation should be in Japanese, matching the language setting

Additional Context

• Related closed issues: #23592 (closed as dup of #4866), #4866 (static UI i18n)
• The explanation model is already generating natural language — adding a language instruction to its prompt should be a minimal change