I did the "easy" route - mastering one language of each of the main western groups (Germanic, Latin, Fenno-Ugric, Slavic) makes learning or at least getting by with the second or third of the same group is easy. With my French base I get by in Italy, Catalonia, Spain even Portugal. German helps me a lot in Holland and in Scandinavia. Speaking Russian makes it easy(-er) to understand most of the other Slavic languages. With Finnish Estonian opens up as well. This of course goes for reading and to a certain extent understanding, not actually speaking, say Catalan or Serbian.

The difficult route - Eastern Asian languages- I avoided. Any Chinese (be it Mandarin or Cantonese), Japanese, Korean I know is limited to some very basic politeness - yes, no, thank you, hello, and of course the names of my favourite local dishes

Should/could I spend more time there, I feel that Bahasa Malaysia and/or Indonesia would open up quickly.