A better translation would be ‘I know what you want to say’
I think you are supposed to use the ‘Report’ feature for things like this, no?
I should have phrased this as a question, as I was hoping for other’s opinions.
True, your version works better as a literal translation.
However, if we were translating from English to Polish, it’s still quite likely that “I know what you’re going to say” would be rendered as “wiem, co chcesz powiedzieć” (e.g. in a movie or a book).
This is simply because Polish doesn’t have a direct equivalent to the “going to” construction, and “chcesz powiedzieć” will be a much more natural expression in most contexts.