I have another post brewing to answer questions raised in comments on the dwarf posts, but I wanted to talk about a couple posts (here and here) on the topic of ditching the common tongue. Like them, I would certainly require the PCs to have some form of common communication, but I'm not adverse to the idea of an adventure in a locale where the PCs have trouble communicating with the natives. But I have some thoughts on this.
Historically, people who don't speak the same language but need to communicate have always found some way to get simple concepts across: direction/indication gestures, shared words for simple needs. And let's not forget pidgins, trade languages, and religious languages. Rudimentary Latin in medieval Europe was used as a trade language and a religious language, by those who traveled, and furthermore was the basis for the languages of the western countries. Lack of a common language prevents teaching (except by demonstration) or conveying history, law, philosophy, politics, or the natural sciences; PCs in a strange land should still be able to buy simple gear, horses, pack animals, or livestock, or get weapons and armor repaired, or find a place to eat, or say something like "via templum?" and get directions to the temple, or "via Dunderhall?" and get directions to Dunderhall, the local dungeon.
I have some ideas for running adventures in a world without a common tongue.
In the random tiny kingdom system I've been developing, it's my intention that each kingdom speaks its own dialect, derived from a common source. The kingdoms are separated from each other except along a common, linear route -- in my case, a river -- and are labeled with a code beginning with an abbreviation for the river name followed by a digit from 0 to 9 indicating how far down the river the kingdom is located. That number is also an indication of mutual intelligibility of dialects; the farther apart two kingdoms are, the harder it is for the inhabitants to understand each other.
Since they're related dialects/languages, if you know one, you sort of know them all, but it takes a while to become familiar with new dialects. Sound familiar? I'd treat dialect familiarity the same way I would treat weapon familiarity: characters must make a weekly Intelligence acquisition roll (saving throw) to become familiar with the local language. Otherwise, all reaction rolls are at a penalty. Actually, since I prefer 2d6 reaction rolls, I would treat the reaction roll as a simultaneous Intelligence save to avoid miscommunication, causing a reaction that's one step worse, until the character becomes familiar with the local language.
For the familiarity acquisition roll, I need to know that location digit (0-9) for the kingdom the character is in and the kingdom the character is from -- or, if the character is an exotic foreigner, the digit for the language of the kingdom the character has learned. I'd have the player roll a d6, add a bonus for high Intelligence, and add the lower kingdom digit; the total must be higher than the higher kingdom digit.
Example: Bob is an Int 13 from Kingdom B3C and is visiting Kingdom B9O (we'll skip actual kingdom names for now, since they're unimportant mechanically.) Bob's player rolls a 2, add +1 for Int, and +3 for language B3C, total 6; this isn't higher than 9 (for language B9O,) so Bob hasn't picked up the local dialect yet. Until Bob does, every reaction roll is also treated as an Intelligence save with a similar adjustment: Bob adds the lower digit (+3) to 1/3 his Int and adds the higher digit (+9) to the reaction roll; if the save fails, a neutral reaction turns hostile.
(I know the way the numbers work look a little complicated, but basically it's a trick to avoid subtraction; instead of using the difference between the two location digits as a penalty to saves and acquisition rolls, I'm adding one number to each side. You can subtract the lower number from the higher and use the difference as a straight penalty, if you feel that's easier.)
If a character doesn't speak a related language at all, communication is limited to simple gestures and whatever local words the player learns. Each season (3 months,) making an Intelligence acquisition roll, modified for total duration of exposure (I prefer adding +1 each time the duration doubles.) Success means the character has learned the language at the basic level.