Speculative decoding will be model/software based and apply to all languages. The time, compute, and energy will be less compared to other models, but for the same model, hardware, and software used my reasoning still applies -- comparing English to other languages (unless optimized by the tokenizer) then English will consume less tokens and thus less energy. That is, it is still a function of the tokens used.

roughly the tokenizer is optimized such that the training data (for the tokenizer) can be represented with the smallest number of tokens. and yes, English tends to be overrepresented in training data.