op would be conversational with a significant part of the world, and they're not to blame for colonialism. just by learning spanish, english and portuguese they would be able to talk to anyone south of rio grande in the u.s., and talk to some former british colonies in africa and asia. put some russian and french and you would be left with just perhaps middle east, east and southeast asia.
knowing that and learning some arabic and chinese (throw in some language of some east or southeast asian country if they want) and there's not much left, but to discuss how colonialism brought the world to this situation.