Support for using multiple translation APIs concurrently for load balancing

[Mahdi7b]

Hi,
First of all, thank you for your great work on Subtitle Edit.

I would like to suggest a feature that allows users to define multiple translation APIs (e.g., DeepL, Google Translate, Azure, etc.) and have Subtitle Edit distribute translation requests among them, either in round-robin fashion or based on load or availability.

• Why this is useful:

• Many APIs have rate limits or usage quotas.
• It would help balance the load when translating large subtitle files.
• If one API fails temporarily, the others can be used as fallback.
• This would be especially helpful for users using free or limited API keys.

• Possible implementation ideas:

• Allow users to define a list of API keys for each supported service.
• Provide an option to enable load balancing or fallback behavior.
• Optionally show which API was used per segment.

Thank you for considering this!