Jetpack AI Assistant generating feedback in Spanish, not English

### Impacted plugin

Jetpack

### Quick summary

The user reported that, within their post, the Jetpack AI Assistant is generating feedback in Spanish, not English.

I confirmed the issue, please see:

https://github.com/user-attachments/assets/5ba36b8d-e5c5-4f5e-af0e-517d9cc370d3

### Steps to reproduce

1. Edit a post
2. Open the Settings sidebar
3. Click the 'Generate Feedback' button.

- The feedback is generated in Spanish even though the site language and interface language are set to 'English'

- Please see this video:

https://github.com/user-attachments/assets/f2117de4-9ab5-4256-8ce8-166a4fb06844

### Site owner impact

Fewer than 20% of the total website/platform users

### Severity

Minor

### What other impact(s) does this issue have?

No revenue impact

### If a workaround is available, please outline it here.

I suggested the user make use of the browser translation tool to work around the issue for now: https://tinyurl.com/3n4tuvwt

### Platform (Simple and/or Atomic)

Simple

Start with the Jetpack AI Assistant's “Generate Feedback” entry point described in the reproduction steps, then trace how the site and interface language are passed into feedback generation. Reproduce the Spanish output on an English-configured site and verify that feedback is generated in English afterward.

Written by the indexing model from the issue text.