feat: add-custom-translation-prompt

[senlinyy]

This PR adds customisable selection-translation instructions, so we can add more custom instructions like being more natural in translation, adding more contextual explanation, or explaining a single word in a broader context, etc.

[Visterainer]

Thank you for your contribution and for looking for ways to improve the selection translation experience!

After evaluation, this PR will not be merged. Selection translation in AIdea is intended to provide a quick and faithful translation of the selected source text. Its behavior should therefore remain simple and focused, without introducing a separate custom-instructions setting.

If a different translation style, additional context, terminology clarification, or further refinement is needed, it can be requested directly in the AIdea conversation. For example:

• “Translate this in a more formal academic style.”
• “Explain this sentence based on the context of the paper.”
• “Translate this while preserving the technical terminology.”
• “Polish the previous translation.”

Personalized requirements can also be configured through the existing cold-start prompt, so an additional setting specifically for selection translation would duplicate existing functionality.

Thank you again for the contribution. The implementation itself is complete and thoughtful, but it does not align with the product direction of keeping selection translation simple and focused. Therefore, this PR will be closed.

[senlinyy]

Appreciate the reply. I’ve built this locally and have been using it since then. A few things I’ve found quite useful are being able to add custom instructions to:

1. Not necessarily follow the exact wording, but translate it in a more natural way.
2. Give a short summary after the translation in simpler, more straightforward language.
3. If I select a single word, expand on it and explain its meaning based on the context.
4. Add extra explanations for abbreviations.

It's true that this can definitely be achieved through a sidebar conversation, but having custom instructions specifically for selected-text translation is much more efficient. I also prefer to keep these translations disposable and use them mainly to help me understand things while reading, while the sidebar can be reserved for deeper discussions in general.

It would only require a small settings area, disabled by default, and would simply use the default prompt when no custom instructions are provided.

So, if possible, maybe give it a try and reconsider adding this extra setting. I think it would definitely improve the UX.

Many thanks!