So on my project there will be an options menu where you will be able to select things like language. When I change the language from, for example English to french, how to I change a variable that says the language is now this, so play the music language instead of this one?
localization is a discipline beyond the scope to cover in this space. In general though, “game-wide” could be something you declare as static and not necessarily inherit from Mono. A class might have
class myGameWideClass
public static string currentLanguage
which any class/script could read from and use with
myGameWideClass.currentLanguage
without needing to establish a GetComponent reference.