"If all sessions are in English there's no point for people who only
speak French, Arabic, Portuguese and a bunch of other African
languages but no English to go to that conference."

I don't get this part. How can I, an English speaking person, organize a session and speak Original Arabic? How?

Sessions are open for application. Whoever applies, and is picked, speaks the language he/she is comfortable with. At the end of the day, its not up to the WikiIndaba organizers to generate Arabic or English sessions. The speaker of the session's language is what determine the language to be used. Of which many who came from Tunisia and Egypt who are damn fluent in French and Arabic, but speak little in English, all decided to speak English, as they spoke to people from other parts of Africa.

There are no grammar ninjas at the conference to patrol what mistakes others make.

Samuel Guebo, ABir, Habib and Ouda, all had wonderful stories to share at wiki indaba. English is not their first language. These guys, for the benefit of all, decided to use a language that we all could hear. They could have spoken their various local languages, of which I think no one could have questioned them why, but they shared with all their lovely stories in a way all could benefit equally, of which I really appreciated.

So yes, the session language is dependent on the speaker of that session, however, many decide to use English.

Thus the next conference, you are free to apply to handle a session, and you're welcome to speak French. No one will penalize you for that.

rexford | google.com/+Nkansahrexford