I found the phrase “to mix words” mentioned in a thread from last year as an example of a mangled expression. Nobody commented on it; presumably it was offered and accepted as a corruption of “to mince words.” But I just read something British that used the “mix” formulation in what seemed to be a somewhat different sense.
So: where are you, which do you hear, which is correct, and what exactly does it mean?
Middle Tennessee, it’s “mince words”, almost always in the form of “don’t mince words” or “I won’t mince words.” It means the speaker was (or is going to be) bluntly honest and not use euphemistic language to tell you something.