No. It isn't.
'Don't' and 'I'm' and 'isn't', for example. are contractions that are also correct informal written English. 'Wanna' ( and 'gotta' and 'gonna') are NOT acceptable features of written language. Please do not believe anyone who tells you otherwise. Please don't think that 'wanna = want to' in the same way as 'Aren't = Are not'. This is not true.
Then what is 'wanna'? It is feature of speech only. When native speakers say a sentence like 'I want to go' in a relaxed and fairly rapid way, it sounds like 'I wanna go'. We don't deliberately say 'wanna'. The words in our heads when we say this are 'I want to go'. 'Wanna' is not a word - it's just a sequence of syllables that occurs in connected speech.
So why do we see the word 'wanna' written down? We write it down when we want to imitate speech. For example, if someone in a film screams 'I wanna be free!', then it's acceptable for this to appear in subtitles. Likewise, with song lyrics, or cartoon captions. Or maybe in a short text to a friend, when you want to be funny and friendly. But that's all.
Many non-native learners of English believe that if they write 'wanna' in all their sentences, their English will look 'cool' and informal and natural. It doesn't. Browse a little on this site. See who writes 'wanna'. You'll see that it is only non-native learners. Don't copy them. Write proper English.