It's possible to learn to write in English but with wildly inaccurate pronunciation
that's the tougher way if you want to learn to speak conversational English fast, it will take you longer to learn the pronounciation and speech if all you know is the text book. apart from a few exceptions such as choir or quiche etc., there are a few simple rules to follow in order to get to know how to say things in English. now the accent is another thing...
speak English well but with very bad spelling
that would be a big part of British population ha ha :D, yeah this is very common, especially writing down things in English the way they sound in Polish, such as aj lajk or gud etc., not saying that
bad for everybody, just so you have an idea. people learn English cos it's everywhere, tv, songs, you can hear it all the time and that's how you pick it up. if you lived in UK for some time with no English skills you will pick things up from conversations or the media, but grammar and spelling is essential, just to understand the language and how it works instead of learning it by hard and limiting your vocabulary only to things you overheard.
of course the combinations of the above are there as well, depends on the level of spelling and pronounciation. my spelling is on a much higher level than my pronounciation, i speak clearly but i often say things not quite right or if i'm in a hurry i get the tenses wrong. but i realise i made a mistake straight away once i've done it lol.