How do you tackle language differences between characters? How do they communicate? How do they overcome it?
I love xenolinguistics, so I've explored different options. These include:
* A dominant language that almost everyone speaks, and anything else they may speak is a secondary language. This scenario is more prone to linguistic abuse (e.g. beating children for speaking a heritage language) and more vulnerable to knowledge gaps (e.g. the cursed item says DANGER in foot-high letters that nobody can read). This is how English has treated indigenous and foreign language speakers in several places.
* A popular language that lots of people know but is a first language for the dominant group and a second (or third, or eighth) for everyone else. This creates a different pattern of misunderstandings, because people will think they understand when they've missed a nuance, or will exaggerate their understanding so people don't think they're dumb hicks. This is a problem English currently has as the international air traffic language.
* An auxiliary language that is usually or always learned as a second (or later) language, so that most or all of the characters speak different native languages. Communication runs slower because everyone is translating in their heads, but occasionally you'll find a native speaker who's a huge asset. This happens in far-flung trade networks that cross many small language territories, as in Hand Talk/Plains Indian Sign for a Turtle Island trade network that once spanned all four coasts, although the densest sign activity was (at the time of the European invasion) clustered in the plains. And it let deaf folks hand-talk with everyone, which was a big advantage in trade..
* No single "world language" but rather supraregional or regional languages. Frex, English is a world language, while Turkish is a supraregional language spanning several countries in southern Europe and the Middle East. The farther distance an epic quest covers, the more likely this is to happen, especially if they have to collect items from different cultures to complete it. Using Europe for an example, characters might begin in the far west where English is dominant, swing north (Dutch), back down and go east through French, German, dip south where Italian and Greek are common, and wind up either in Russian or Turkish speaking territory. You absolutely need a character who speaks each supraregional language your party will traverse, and each in turn will go through phases where they can or can't speak the local vernacular.
* There is no single language shared by the whole party, but everyone shares a language with at least one other party member. The smaller and/or more isolated the language territories, the more likely this is to happen. You also see situations where most people speak several languages and switch among them readily; in Europe, people may not share an everyday language but most will try out their other languages to search for a shared secondary one -- that's actually in 20,000 Leagues Under the Sea, although it doesn't help because the Nautilus crew are speaking a constructed language. In this case, the party will be bound not by a single common bond but by tighter bonds between characters who share a language, looping loosely through the whole party from one cluster to another. It creates shifting alliances.
* A party member who serves as a translator. The other members may not be able to speak with each other and/or the surrounding cultures, but the translator knows some widely spoken language(s) that will facilitate communication and travel. A famous case is Sacagawea guiding the Lewis and Clark party. This creates a deep vulnerability where the party's success and even survival rests on one person.
* An artificial translator of some sort. In science fiction, it's usually a device; in fantasy, it's typically a spell. But either can have someone who just naturally knows or can learn all languages, such as an android or someone with the Gift of Tongues. Of course, these are prone to malfunctioning in various ways.
* If none of the above options are available, then party members will not be able to communicate easily. This is most likely in situations that throw together people who would not normally meet each other, such as captives on a slave ship or national heroes suddenly facing a global threat. They must then find a way to communicate -- either choosing a language that one person already knows and teaching it to the others, everyone learning a new language, or coming up with some sort of collective pidgin as has happened on many islands. It's a wonderful way to make everything harder for the characters.
All of these are possible. Most writers want to avoid the issues of language diversity, much as they often avoid issues of racial or other diversity. But changing the nature of language challenges in a story changes the type of story you can tell, because each situation creates different strengths and weaknesses leading to different plot complications. So a wider diversity of language challenges in epic fiction leads to more different kinds of story that can be told, and less repetition that leads to readers thinking, "Been there, done that."
Most stories are about something other than language, so using more than a little language detail can become a distraction. The more mixed the cultures, however, the more significant language tends to become. If it's there and you gloss over it, the results tend to be bad. Then there are stories about language itself -- linguistic science fiction, xenolinguistics, milieu fantasy, and so on. These are the places to bring in the versions above that create bigger linguistic challenges for the characters.
Imagine that you have a bunch of little countries at one end of a continent and invaders from the other. The surviving heroes must band together and stop the invaders. Someone has obtained materials about the magical language of the invaders revealing a key weakness held in their distant homeland. The party members must: 1) get along with each other well enough to survive travel hazards, 2) learn a new language unrelated to any of theirs, 3) and also learn magic, 4) cross the continent, 5) defeat the invaders using their new knowledge, and 6) return home to deal with the changes all this has made in their lives which now set them apart from everyone they knew and loved.
If they had instead one person who already knew the target language, or a device that allowed any of them to read it, or they needed to capture an invader and somehow induce the captive to act on their behalf, those would each be very different stories. And that's how language shapes literature.