Translation:Gratis boeken zijn goed.
If it's plural, why gratis and not gratise?
According to my Dutch housemates it is an exception, always use "gratis" regardless :)
Borowed words are weird
It is gratis because it is a Latin word, not a Dutch one.
Why is goed not plural?
Goed is an adjective.
Is kosteloos wrong?
You could use kosteloze, however, note that gratis is more commonly used.
Why not "vrije boeken zijn goed"?
"vrij" means "free" in the sense of "liberated".
"gratis" means "free of charge".
The English sentence doesn't specify which definition of "free" is meant, so both translations should be accepted!
Because you do imprison books?
I don't, I believe in books being free! :)
Anyway, I had a message earlier saying this translation is now accepted too.