From the instructions for the CSV import:
"Speaker (separate multiple speakers with commas)"
"If you are presented with options on export, fields should be
delimited with a comma, and enclosed with a double quote (")."
From an email from a user: (thanks Michal!)
So, if I have two speakers I should separate them by comma and than
enclose with double quote (eg. "Darek Górecki, Rafał Nauka"). But it
didn't work, I've got the "Error: Language 10:45 not supported" error
(see attachment). This was probably caused by parsing speakers as two
separate fields. The error message itself could also be more
descriptive, eg. you could put talk title there.