I have been working on something for a new campaign based on the lack of world spanning common tongues over several of my past campaigns where I have had problems from being too detailed about it.
Alot of it comes down to your campaign setting, the size of the world and the 'play' area, continents and other geographic features that could possibly demarcate a language variation and then theres planar consideration too, alt primes, outerplanes, inner plane versions of humans, dwarves, elves and whatnot.
But for a single world setting I think the best bet so far is to have for humans, which in most settings are the most widespread race with most variation have maybe 2 or 3 base languages, dead languages, now called the ancient tongues, used by scholars, and/or preists, and/or mages, But possibly not so dead, large empires might use one as the official legal language for court and government documents. But with those 2 or 3 trees you can easily break down your human cultures and georpahic regions into numerious 'local' languages and/or dialects. Or maybe depending on how the world was created, how the gods did their thing there, there might be but a single ancient tongue that all the human languages are based on.
For the non-human races it tends to be easier to say there is but a single base language, ancient tongue. Then each sub-race would have its own langauge or maybe just dialect of that base tongue. Its possible for a sub-race to even have its own tongue based off the language of one of the other of that races sub-races. And just like humans you would want to add in variation for location and culture across the continent or major geographic demarcations. (The wild elves living in a 'lost valley' for two thousand years are unlicky to speak the same exact language as the group of wild elves three thousand miles away in a forest and have had contact of some sort with other elves and races over same two thousand years for example). And of course you probably want to have a couple of different trade/merchant pidgin tongues too, but depending on your setting maybe the various trade tongues are just such and such empires national langauge.
If your plotting out various kingdoms, cultures, regions its not that much extra effort to setup langauge variations for those races while your at it. For dialects maybe the written language is all the same for a single language, and for those languages whose written form is runes or 'picture' words maybe even with the spoken form vastly different and requiring hard study to learn the 'written' form might still be the same.
The part I am still working out is the game mechanics of it and what might allow for feasible use in a game without frustrating the more hack-n-slash oriented of my gamers without making it pointless for the role-play inclined of the gamers.
My thoughts are to allow the player at each level their INT bonus in langauge skill points. And instead of the extra languages at 1st level based on INT bonus convert those to language skill points and give it some type of modifer based on class same as normal skill points. So priests, mages, rogues and nobles for instance would have a higher bonus multiplier at 1st level over fighter or barbarian.
Then following along the lines of the KoK rules the more skill points in a language the more fluent you are. Your 'home' langauge you get for free say 5 points if we're using 5 points as the basis for the common native speakers level of education/fluency. Also a dialect or regional variation on a langauge would not have its own language skill and points, it would still be considered the same langauage(say someone from new orleans and someone from new jersey)
Then you would have opposed rolls or DC rolls when speaking with someone of another langauge or a dialect of the same language, and get a synergy bonus for each langauge that you know that was related to the langauge being used.
For example, we have Famer John and Farmer Smith both living within the boundaries of a large country we'll call Nation A. Both speak the same national langauge. However Farmer John and Farmer Smith both speak a different dialect of the same language. Both are commoners and considered to have 5 skill points in the language of Nation A. Since its the same language we make the DC 10 for them to understand each other. Farmer John only has an INT of 10, while Farmer Smith isnt so bright and has an INT of 9. So Farmer John gets to add 5 to his roll to understand Farmer Smith, and Farmer Smith gets to add 4 to his roll to understand Farmer John. If they both make their rolls their able to communicate as surely as if they both lived in the same area. But if say Farmer Smith missed his Dc check but not Farmer John, then we can assume Farmer John understood Farmer Smith fine, but that Farmer Smith misunderstood some word or its meaning, the greater the differance between their final adjusted rolls the more misunderstanding he had. It would be up to the GM to decide what failed in the communication or if Farmer Smith percieved an insult or whatnot. Maybe the greater the differeance in the rolls you step through the degrees of reaction, friendly to neutral to angry to hostile. Maybe a friendly misunderstanding, that is to say Farmer Smith knows he is missing something and not sure what but he knows it and is not offending or too upset, so he keeps on talking letting Farmer John know he didnt understand something he just said and he repeats hiomself or rephrases and they make another roll to see if he understood. A hostile reaction might mean Farmer Smith thought he was insulted in someway or challenged and he is so upset about it that he takes a swing at Farmer John, or stalks off.
Now for two langauges based on the same root.
Farmer John's and Farmer Smith's home tongues both share a root tongue which is Language A. Both have the 5 in thier home tongues. And Farmer Smith still isnt so bright so has that -1 for INT. They've both met up in an Inn while traveling somewhere and are sharing drinks and making idle chat, hello, how are you, hows the wheather back home, hows crops and such so we make the DC 10 because its just small not too complex talk. Since thier langauges share a common root they get a synergy bonus of 2 for each having 5 'ranks' in their home tongues. Farmer John gets a +2 to his roll and Farmer Smith only a +1 because he isnt too smart(-1 for INT). So though in this case its harder for them to understand each other its still possible. And of course you might add in reaction modifiers and such not and if the rolls are too far apart then things like CHR and other skills might mitigate the more hostile reactions to misunderstanding.
Say we have Adventure John and Adventurer Smith though, John with an INT bonus of +2 and Smith with no INT Bonus. John speaks 4 langauges all with the same root tongue and Smith speaks 2 languages with the same root tongue, both have 5 ranks in all these langauges. They both would get a +2 sysnrgy bonus for EACH of the related langauges they know. So Johns bonus to his roll would be +10 total (+8 for 4 languages) and Smith's would be +4. Know if their just sitting in the Inn's common room sharing drink and idle chit chat we might make the DC 10. If however their trying to discuss the political situation in the kingdom their traveling through or maybe swapping fighting tactics against orcs maybe that DC would be 15. If two alchemists where discussing brews maybe the DC would be 20 or even higher.
Anyhw even if they both make their checks oyu might want to tally the differance and use it for 'reactions' to help determine the tone of the conversation.
Depending on the itital reaction values maybe the conversation only requires a DC roll once be the conversation 2 minutes long or half the day. On the other hand maybe the attitudes and such make you decide it would be better to make checks every couple of minutes of the conversation, thus allowing the players use of their diplomacy, bluff, innuendo or other Charismatic skills to help soften a situation that started out with swords almost at everyones throats.
Two diplomats trying to converse over a language barrier on a treaty for instance you could have them make continual checks and base the npc's reactions on the differance in the rolls wether they failed or succeded, which would give oyu some baselines for making talks go from friendly to suddenly strained to having to try to smooth things out and back on course.
By regulating the number of times you require the rolls to be made and how much you allow reactions to influence the conversation along with the 'diplomatic' type skills you can probably keep your hack-n-slashers and role-players all happy. 1 or 2 checks when trying to get directions from someone on the street to having checks every couple of sentances(affecting the npc reactions each check) as you and the players talk out their encounter with the city watch as the group was caught crawling up out of some sewer grate.
Anyhow, I am still fleshing things out and probably my long rambling style of talking ( i tend to type as I think instead of think first then type it up later) doesnt help any, but so far this seems that in practice to be very flexible, it doesnt eat up the players skill points, as they get language points each level based on INT, though of course they can apply normal skill points to langauges too if they want and the GM can make the checks minimal or frequent depending ont he situation of the encounter or even the mood of the player group at the time.
I am also thinking for writing languages that you simply burn a single langauge point or normal skill point and then you ability in writing/reading that language is based off your spoken language score. Back to Farmer John, since he speaks a dialect of Nation A's tongue, he still writes it the same as Farmer Smith would and so there would be no need for a roll, to understand what the other wrote, take 10 on the check basically. But if say Farmer John came across a diary of the local Mage and he was writing about some esoteric arcane things maybe the DC would be 15 or 20 for Farmer John to understand what all the words were or maybe to just get the gist of what he was reading even without understanding what all those 'fancy' words are.
Anyhow, theres my two cents worth, any of the others who got rid of common tongues or are thinking about it care to make comment/suggestion, additional ideals on it?
If your one of those folks that thinks the common tongues and langauge system of D&D is fine as is feel free to stay shutup
I am looking for constructive feedback to flesh out my ideal not someone saying the D&D langauge system is fine as is or that I am being silly or stupid or going to bog my game down. It makes no sense for settings like FRCS to have all those regions and different langauges and cultures if everyone from some village dunce in the The Great Dale to an orc in some abadoned dwarfhold deep in the western Spine of the World can talk to each other.