[riffraff]

written and spoken are quite different at the point of understanding, but mastering written language implies understanding grammar and vocabulary, and that does help with speak too (modulo tolerable pronounciation).

What I mean is, in an absolutely personal opinion/experience:

I still have big troubles understanding spoken hungarian in contrast to written, although pronunciation matches written almost 1:1 I just can't tell the difference between ü u ú Ű) etc.. but at least I can sort of express myself, even if I do it by mispronouncing most words.

So, written does not imply spoken, but it does help.