I've checked and yes, it does seem both spelling coexist... Wikipedia does list "Gothenburg". I have a feeling that "Goteborg" might be the way swedish people "think" it's spelled in English and that it kind of contaminated other people.
What can I not understand is why must exists alternatives of the same name in every language? I can understand to be a little bit modified when the language has not the original letters. But, as an example, from Deutchland til Týskland (how the Faroese people say) is long way... Same with Göteborg, could not be, simple, Goteborg and nothing else?
Was just an opinion I wanted to share, I did not want to make any comment to the translation....