Translation:The library wants to increase the number of books.
English isn't much better at these things if you consider a word like "should". It can have either a suggestive meaning ("He should do some work") or a meaning of guessing ("He should be working"), depending on the context. :)
The secret is that ville isn't used all that often to indicate the future. Mostly you just use the simple present and say "Biblioteket øger bøgernes antal", especially if the context mentions a future timeframe. On the other hand, if you want to emphasise the desire to do something, you can use "ville gerne".
Not trying to be rude, but I'm a native danish speaker, and it's called "Biblioteket øger bøgernes antal". You can't say "antallet" in this sentence. Hope this helps :)
And it's so cool, you're at level 22. Keep up the good work. :D I'm learning Spanish, and I wish there was a course from Danish to Spanish or vice versa.