My players have invested in langauges many times over the course of the game. I tend to drag them all over the small world they live in. Comoon is Common not ubiqious (Sp?). When in the dwarven nation only a few merchants and clan leaders speak common everyone else spoke dwarven. They only spoke common when addressed in common. Most the players took dwarvish when they knew they would be heading that way. they also all took draconic to have a secret langauge amongst themselves figuring it would be a useful langauge for that not having run into a lot of draconic speakers. They have also taken them for roleplaying reasons, the scout rogue/fighter took several humanoid langauges because he figgered as a scout he would need to knwo what they were saying when he spied on them. heck the Bard has taken langauges just so he could Curse the opponents fluently.
Later
Later