In general languages in the Majestic Wilderlands are one of the few areas where I don't get very detailed. My approach is basically that taken by Stargate SG-1. Just about everybody speaks english except in the few instances where I think it would add to the plot. This boils down to two circumstances
In Stargate SG-1 the biggest foreign language is Ancient which Dr. Daniel Jackson is the party's err SG team's expert. This followed by G'ould and Jaffa which are sprinkled throughout for flavor.
Likewise I usually only use the language barrier in limited circumstances. Isolated cultures mostly barbarian and handful of demi-humans. Ancient languages not commonly spoken anymore. Another use is when a bunch of PCs share a language in common that is not spoken by the local to talk without being understood.
Now just because I don't get detailed in practice doesn't mean I don't have notes on the topic.
Languages of the Majestic Wilderlands
The most static of all the Wilderlands languages. Sounds very formal to most speakers of elven influenced languages. This is one of the languages used as a foundation for the common tongue.
This covers a variety of human and halfling dialects that are heavily influenced by elvish. Nearly all are mutually understandable although speakers from widely separate geographical areas will have thick accents when trying to talk to each other.
Gnomish is a dialect of Dwarvish and mutually comprehensible. Dwarves and Gnomes from widely separated geographical areas have a hard time speaking to each other. The writing is still at a high level of comprehension. In another millennia these dialects will be effectively different languages.
There are nearly two dozen variety of Orcish languages as the short generations cause rapid changes in language in different geographical areas and even from tribe to tribe.
The original goblin language has been largely subsumed by a patois between it and Viridian. Currently it is a dialect of Viridian and mutually understandable with Viridian speakers. It is considered a mark of low status among Goblins.
The language of the Elessarians dominate much of the Northwest Wilderlands and the Padizan peninsula. Old Elessarian is now a dead language similar in use and status as Latin in the real world. Elephand is the successor to Elessarian in the Kingdom of Dunador. It has heavy Elvish influence. Common(Viridian) is used in the Viridistan Empire. It is a hybrid of Viridian and Elessarian. It is comprehensible with other Common tongues. Elessarian is used in the Padizan Peninsula and as different to Old Elessarian as Italian is to Latin.
The Ghinorian Language was spread throughout the Majestic Wilderlands by the Ghinorian Empire. After the fall of the Empire it split into several dialect that are evolving into separate languages.
Old Ghinorian is the pre-imperial language lost during the time when the Ghinor valley was subject to repeated barbarian invasions. It is now used as a high church language of the Church of Mitra.
Imperial Ghinorian is language used when the Ghinorian Empire was created after the invasion. The Church of Mitra uses this a ecumenical tongue to allow adherents from different lands to communicate.
Northern Ghinorian is spoken in Nome, Dearthmead, Nomar, Modron, and Tarantis. It evolved from Imperial Ghinorian during the existance of the Restored Ghinorian Empire.
Western Ghinorian is spoken in Tlan and Lenap. Although the two region have distinct dialects.
Ionian is the language dominating the Ghinorian Heartland. It combination of the language of the Ionian barbarians that brought down the Ghinorian Empire and Imperial Ghinorian. To make matter more confusing speaker of Ionians call themselves Ghinorians.
Common(Ghinorian) is spoken in City-State and throughout the Tharian Confederation it rose during the Dragon Empire and is a fusion of Elessarian and Ghinorian. It is understandable by both languages and with Common(Viridian). It is evolving with the addition of many Tharian words.
Tharian is the language of the Tharian Overlords of City-State. It is under assault with only the Tharians of Thygamus and the Tharian Coast speaking it's original form. Most Tharians of City-State are abandoning the language in favor of Tharian flavored Common(Ghinorian)