This has happened before.
Obviously, he knew Swedish allready.
A Norwegian back-pack traveller fell and banged his head, while exploring in China. Due to his allready unpredictable and quite erratic personality, it was even more difficult for him to track his own story down, but he was basically a multilingual Norwegian explorer, knocked himself out cold, woke up with amnesia, and no clue which one of the myriads of languages he knew was his own