Some say 'say junk English' is not good, while others think 'say junk English' is imformally acceptable, although 'speak ' here is always good English.
What do you think of 'say junk English'?
I don't have a precise idea of what you mean by 'junk English'. Perhaps you mean slang, sometimes unheplfully called 'bad English'. Slang is OK in the right context. (But, if you do mean slang the verb should be 'use' or 'speak in', and not 'say'.)