španska sela

1. colloq. all Greek to me
   Matematika? To su za mene španska sela. — Maths? It's all Greek to me.
   Kompjuteri su mojoj baki španska sela. — Computers are all Greek to my grandma.

Usually in the construction to su nekome španska sela. Both sela and the verb su are plural even when a single topic is meant: to su mi španska sela, "it's all Greek to me".