Multilingual Typing for Czech and English (bilingual on one keyboard) not supported?

I switched to an iPhone, from Android, almost a year ago and still can't figure out how to get this to work. Is simultaneous bilingual typing on one keyboard (without having to change the input keyboard manually) not supported by iOS?

I frequently type in Czech, English, Russian, and sometimes Italian. But mostly Czech and English, which I might switch back and forth within one message multiple times. Even if I have just two keyboards, as I type fast switching between the language input (with the globe icon) I inevitably make a mistake and then the autocorrect just messes up the whole text because it thinks am writing Czech while I am writing English or vice versa.

Is there a way to set this up, or is this just not supported on iOS?

I have been using this feature on Android for over 10 years, so I am puzzled that iPhone doesn't have it.

Will this be supported on the iPhone, and if yes, then when?