[FEATURE]: Add message translation for Windows desktop app - left-click to translate foreign language messages

[LifetimeVip]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Problem

When using OpenCode, the AI sometimes outputs content in other languages (Japanese, Korean, Russian, etc.). If a conversation contains foreign text the user cannot understand, they currently have to manually copy and paste it into a translation tool, which disrupts the workflow.

This is especially painful for Windows desktop users who lack browser extension-style translation support.

Proposed Interaction

1. Left-click and drag to select a portion of text in a message
2. A floating mini toolbar appears near the selection, with buttons for "Translate", "Copy", etc.
3. Click the "Translate" button to translate the selected text
4. Translation result is displayed in a tooltip/popover bubble near the selected text, with a close (x) button
5. Click outside the bubble or press x to dismiss
6. Alternative: Right-click context menu also includes a "Translate" option

Settings

Add a new setting:

• Name: Translate Target Language
• Default: Auto (follow system language) - automatically detects the Windows system language as the translation target
• Available options: Chinese, English, Japanese, Korean, French, German, Russian, and other common languages

Notes

• Code block content should be skipped or labeled as code to avoid meaningless translation
• Translation results should be cached locally to avoid redundant API calls
• Support both local models (e.g., Ollama) and cloud APIs (e.g., DeepL, Google Translate) for translation

Use Cases

1. User asks in Chinese, but the AI response contains Japanese code comments or documentation
2. Code snippets include non-native variable names or comments
3. Multi-language team conversations contain mixed languages

[github-actions]

This issue might be a duplicate of or related to existing issues. Please check:

• [FEATURE]: 模型在中文对话中应自动翻译英文术语，不应假设用户懂英文 #25783: A previously closed issue by the same author requesting automatic translation of English terms in Chinese conversations — similar theme of language translation within the app
• Translating promts to english befor doing the job #23077: Asks about translating prompts to English before processing — related concept of in-app language handling
• [FEATURE]:i18n support #7170: Open feature request for i18n/localization support — overlapping scope

Please review these issues and clarify how this request differs, or consider whether this could be tracked under the existing i18n request (#7170).

[LifetimeVip]

Thanks for the references. This request is distinct from each of those:

• [FEATURE]: 模型在中文对话中应自动翻译英文术语，不应假设用户懂英文 #25783 is closed and asks the model itself to auto-translate English terms in Chinese replies — a model behavior change, not a UI feature.
• Translating promts to english befor doing the job #23077 is about translating user prompts to English before sending to the model (pre-processing), not about translating conversation messages the user reads.
• [FEATURE]:i18n support #7170 tracks i18n/localization of the app's own UI strings (menus, settings, etc.), not translating conversation content.

This request is specifically about a Windows desktop UI interaction: the user selects text in a message via left-click drag, then a floating toolbar with a "Translate" button appears, translating the selected message text into a configurable target language (default: system language). It is an on-demand per-message translation UI feature, unrelated to the above.