A Con Lang (or just "conlang") is short for "constructed language", e.g. a language the writer, their friend, or some other associate has made up for the purpose of using in a book or show. No, they did not just say that the Alien/Elf/Bee People speak a different language, they actually made up an exact vocabulary and grammar, one that can be translated into English (or equivalent). This is where Translator Microbes are abandoned and a dictionary given to the reader.