as a "polyglot", I find typing english the fastest, purely because pretty much all of my internet activity is conducted in english.
I type chinese slower (per word), but because chinese condenses information much more heavily, I convey roughly the same units of information in either language.
french words are generally longer and therefore would take more time to type.
unfortunately, I do not know steganography, but if I did, I would be able to type english much faster