In my current campaign, the "civilized" (PHB races) lands are a quarter of one continent. The rest of the continent (and possibly the world, we aren't there yet!) is loosely settled by "the Tribes": all the goblinoid races, plus pretty much all the giants. The Three Kingdoms speak a single tongue - Kingspeech, aka "Common", for lack of a better term - but each has its own "accent". Within the Kingdoms, the dwarves and elves are both part of the cosmopolitan life and have some reserved locations for themselves (Alfendark Forest for the elves; Kagh Da'ruhm and the Blackrock Cliffs for the dwarves) where only the racial languages are spoken. Other PHB races... speak Kingspeech, as they no longer have a distinct racial identity.
The Tribes all use Goblin as their primary tongue - essentially "Tribal Common". Like the Three Kingdoms, Tribefolk from different areas have different accents, but can still generally make themselves understood with minimal confusion. (The Giants still maintain their own tongue, and each subtype of Giant has its own dialect and accent that is clearly distinct.)
For Story reasons, there is only one other language, that of the "Ancients" that came before both the Tribes and the Kingdoms.
I thought long and hard about giving each Kingdom its own language - and thus giving PCs a reason to learn something other than Common, Goblin, Elven, Dwarven, or Giant. (Ancient can't be learned by a starting character.) But I decided it would a layer of complication that wasn't required for the game. Likewise, Goblins on the west side of the Terrorspine Mountains are mostly separated from those on the east side (where 90% of the campaign takes place)... but emphasizing those differences wouldn't bring enough to the game. [Should the campaign end up on another continent though... I'll make that as a key distinction making the place feel even more foreign.]
In a past campaign, I tried to make cultures and regions very distinct, even down to different coinage. Elven coins doubled as jewelry, dwarven coins as weapons and tools, modern coins were different sizes and metals from recovered coins from lost ruins. Moneychangers took a cut of conversion, but PCs could also seek out collectors who would pay more than certain coins' worth to complete their collections... It was interesting initially, then fell by the wayside, just like tracking arrows and days of food often does in most campaigns.
Nowadays, I emphasize visible cultural differences - styles of dress, customs of eating, what is considered "good manners" - and local specialties. Alfendark bows are comparable to the enchanted works from the Ruby Tower... but the juffawood from the pirate islands hit harder. Marihan polearms are the best in the world, but if you can get an Alfendark wordsmith to craft you a spear, it will be much lighter. Klathos is known for its sapphires and copper, while the Jendaran Empire to the south produces the best alchemical goods and leather. And only the dwarves of the Blackrock Cliffs can make "boomsticks"...
But they all speak a variation of Kingspeech a.k.a. Common!