AI Assistant: Changing Tone Translates Swedish Text to English

### Impacted plugin

Jetpack

### Quick summary

When using the AI assistant to change the tone of a text written in Swedish (it could be for other languages too), the text is automatically translated into English.

This issue was found as part of Jetpack Testing p8oabR-1ml-p2.

### Steps to reproduce

1. Add a text in Swedish.
2. In the AI assistant, click Change Tone.
3. Select any tone.
4. Observe that the entire text will be translated into English.

https://github.com/Automattic/jetpack/assets/67279475/23e94cc0-2ba2-46b4-af58-e5295c4ffea9

### A clear and concise description of what you expected to happen.

The text remains in Swedish with only the tone being adjusted.

### What actually happened

The text is automatically translated into English.

### Impact

All

### Available workarounds?

Yes, easy to implement

### Platform (Simple and/or Atomic)

Atomic

### Logs or notes

_No response_

Start at the Jetpack AI Assistant's Change Tone flow and reproduce the issue with Swedish text, then trace where the tone request is assembled or handled. Done means selecting any tone preserves the original language while changing only its tone; verify the behavior with the reported reproduction steps.

Written by the indexing model from the issue text.