I have been searching for this and all I can find in the web is that it is not possible to translate the srcset attribute of an image.
Based on the recent trends of web using srcset is widely recommended and Lighthouse is also rates based on loading best fitted images.
I am not sure what is the limitation to implement that but for me if you could provide a way just like you did for the src attribute would work. like find this string in srcset and replace it with the one provided.
This is a becomming a big fallback for our use cases and I am sure there are many customers facing this.