Tok Pisin, a.k.a. New Guinea Pidgin, has exactly two prepositions: bilong, which means "of" or "from" in a possessive or attributive sense; and long, which means everything else.
I have to admit that I was a bit surprised when my ex-wife listed off Spanish prepositions to discover that it excludes a lot of words I would have thought were prepositions but Spanish considers adverbs and only become prepositional when used in conjunction with one of the enumerated prepositions, usually (always?) de.