In fantasy, it's generally an accepted convention that the language one is reading isn't the language the characters are actually speaking. It works as if it's a translation.
When characters speak different languages to each other, it still has to be rendered into the language the reader is reading. Hence, you have the narrative indicate what language the character is speaking.
For example:
'Greetings, old friend. It's great to see you,' Master Chef said to Master Cooper in Berillian. Under his breath, he muttered, 'You old git,' in Selliac.
So unless your fantasy story takes place in alternative versions of, say, England and Spain, you wouldn't say your characters are speaking English and Spanish. You say they're speaking whatever languages they're speaking in your made-up world.
This is simply a convention of SF/F, and if you read carefully, you'll see how authors do this all the time.
Oh, and if you're thinking about making up a language, as Bufty said, keep it to a minimum. Don't try inventing languages the way JRR Tolkien did unless you have his extensive background in languages and philology.