First, sorry for my bad English.
I mean, for example in my case, that would be great to have a different color of the caret for english and russian.
Other users can have second language in the system, for example — german, chinese, polish, does not matter. That is, when you have english selected, then the default color of caret. And when you selected is not english, the other color of caret.
It is very clear and comfortable when you type and constantly switch from one language to another.