Each race is given at least one language that they can speak. Maybe more.
Most everyone can speak common. If you are on the Eldland, and you speak Eldland common - for the most part - you can make yourself understood. But go somewhere else, and you might have trouble understanding.
There are all sorts of new continents that have come into play - language can be important. Jiran Common is not the same as Eldland Common.
If you want to learn other languages, then you need time and a teacher. I figure that learning a language doesn't mean you speak it completely fluently - but there would be various levels that you could build to. Depends on how much you dedicate to learning it - and how much you can practice it.
Uniting landmass languages:
Common - Tivalera
Common - United Isle
North, East, and South Jira
Merchant cant of Jira
Malcovian desert - which is cast driven Stonetalk: Low, Merchant, Lordly
Northern and Southern Alderly
Color Language - Halouakanowa
Jira has a bunch of languages - some of which overlap and others don't. A lot of their war torn history tended to build diversity in their kingdom/region languages - as a way to know who was the enemy.
Tivalera has a bunch of languages. Many of the populace have a few words of Tivaleran elvin, and if you are skilled in language shifts - you could make yourself understood by going that route.
Race Languages: Sometimes mouths and intelligence just doesn't tend to help a race of people/monsters. Sometimes it's a mark of regions and their isolation. Pride and history vi with laziness and habbit. There are a number of languages that are for specific races - Orcish, Xinji Orcish, Darkspeak (demons), Black Zintirny Elvin, and so many more.
Your characters will run into things that do not speak your language.