We played the Reign of Winter AP, which essentially has this problem (mini-spoiler, common isn't as common as I'd like).
The problem was, I was a fighter. I certainly couldn't afford spending a ton of my 2 skill points to learn a language every other session and also diplomacy/bluff to do anything useful with it, nor could much of the rest of the party. And even then, you had to suffer though whatever level you were at until you leveled up to get the darn point to put in it to learn language-of-the-week, hopefully not killing the quest target in the interim.
The result was only one character could actually interact with any NPC in the entire adventure. It was miserable. We often just had to start killing things and hope that was the right answer, since we couldn't talk to anyone to figure out what was going on half the time. And the other half the time the rest of group went for a beer run while the one character that could actually, you know, play the game, screwed everything up (he couldn't afford the point in Diplomacy and had low Charisma).
It was one of the worst experiences I've ever had in Pathfinder, and basically killed the whole AP for me (we had almost zero connection to any NPCs or even the plot).
TL;DR, don't be cruel to your characters (or at least, not to me, please), make common great again.