I would recommend learning at least some basic phrases before going to Romania, however long you intend to stay - outside Bucharest it is more difficult to find someone who speaks English (especially when you are trying - or, rather, failing - to book a train ticket!), although a suprisingly large amount of Romanians do (especially the younger generations).
I found these phrases essential!:
Da - Yes
Nu - No
Cit costa? - How much?
Buna - Hello
Multumesc - Thank you
Nu inteleg - I don't understand
Va rog - Please