I wonder if it's possible to complete the 'alien dictionary'.
I would hope so. To me I see the geography and landscapes of the game as transient - you move through them in pursuit of a goal. But I do hope that goals like fully learning alien languages and uncovering lore are attainable to dedicated players. It might feel kind of useless of frustrating only being able to pick up random words here and there - I think I would prefer to find a species I like and then go on a dedicated self-imposed quest to seek their monuments and learn their ways fully.