Simplify the following text for a Grade 5 native English-speaking person.
Original: Messi then had the most successful season of his playing career , the 2008 â `` 09 season , in which he scored 38 goals to play an integral part in a treble-winning campaign .
Simplified: Perhaps his most successful season was the 2008 â `` 09 season . In this season , Messi scored 38 goals .