[biztos]

I think real-time lookup in a corpus would be enough if it's implemented well.

I'm a non-native speaker (reasonably fluent) in two non-English languages, and when I'm writing, if anything strikes me as sounding "off" then I google the phrase and see how common it is.

In my less-fluent of the two languages, I end up doing this a lot, often just to check my work. As a result I write e-mails and such very slowly, but at a fluency level exceeding my actual fluency in that language. Which seems like a good tradeoff for written communication.

It would obviously be useful to have that done for me while I type.