Pere, who is also the former Barcelona coach's manager, said his brother has been taking classes in German in New York, where he has been living in the past year, since last November.
Pere revealed that so determined was his 42-year-old brother to master the language he brought his teacher to Spain when he returned there for the Easter break.
"It's his (Pep's) style, he is stubborn," said Pere. "Pep always behaves in such a way, he is an obsessive.
"It's absurd. You are with your brother and he doesn't stop talking German with his teacher," added Pere, who was instrumental in drawing up the contract with Bayern which both parties signed in mid-January.
Guardiola, who guided Barcelona to 14 trophies between 2008 and 2012 including two Champions League crowns, is due to take his first coaching session with Bayern on June 26th with his first press conference according to media reports due to take place two days later.
Guardiola has a hard act to follow as veteran Jupp Heynckes guided Bayern to not only the Champions League but also to the Bundesliga title and the German Cup last season, the first time a German club achieved the treble.