Language is important in any series. Everyone in the world is able to speak at least one language. You may want to create a new language or two or three for your world. If you choose to make a constructed language it would be easiest to base it on an already existing language. This will give you a base for grammar and spelling when making your language. You can also try to make your language sound like no existing human languages, however this is very difficult as you will most likely get a language similar to at least a few human languages.
You may also choose to use existing languages in your world. This will make it so you don’t have to put as much effort into making a believable language. You may want to use existing languages in a world which parallels Earth. By using an existing language you make your world less alien while also not needing to create grammar and spelling rules from scratch.
A third thing you could do is make a few words of a language and not go any further. This gives culture to the people in your story and is way easier than making the entire language. Words you would most likely create are title related words such as miss, doctor, and mister, as well as pet names such as honey, darling, and stuff like that. You may also create greetings. The benefits of doing this is that you have significantly less background information that is just going to go to waste. Afterall most if not all stories are written in a human language so most of the time you won’t even see or hear the language being spoken.