A link without a question mark

Rails makes links stay in a nice style for most of time.
But what if a link have to pass several arguments.
For instance, for a book site, would likely to have a link like this
one:
http://www.a-book-site.com/books?category=5?language=2?author=23
this link will show book list that fits every argument.

since it’s an open page url, not a system management one, I don’t want
to POST this arguments, because then this page may be invisible for most
of search engines.

of cause, I can change it to
http://www.a-book-site.com/books/category/5/lauguage/2/author/23
but its seems like a url that sunk kind of too deep . And more
importantly, if I want most of arguments to be optional (some time I’ll
like to check all book that has category=5 and author=23 attributes), as
the number of the arguments grow, change the order of this arguments
will lead to a huge work to fix the route.rb file.

I have seen a solution like this one:
http://www.a-book-site.com/books/category--5---lauguage--2---author--23/
but I haven’t had chance to take it into practice yet. and before that,
I want to know what idea you’d like to share with me?