My ex-roommate didn't know any other language besides English when he started Japanese 1 but near the end of the year, he became one of the top in the class and could converse and write really well in standard Japanese. This year, he's doing Japanese 2 and he doesn't seem worried at all.
Though I can tell you have he studied virtually everyday for the class and studied hard. He's a natural-born genius type so results may vary.