The question of continuity is an interesting one. There was a similar issue for the recent Lord of the Rings and Hobbit movies, where some of Tolkien's languages are very fragmentary but there was a desire to have more invented speech.

David Salo is a Tolkien scholar who was brought onto the film team to help expand some of Tolkien's conlangs for use in the film. While his work isn't strictly "canonical," he did do a lot of serious work to make his additions fit into what fragments we have. His blog is a good read: https://midgardsmal.com/