Hi Armin Saberzadeh,
I think it is quite fine to have the French translations in URLs like www.abc.com/fr/livre.
Though it is also fine to leave it www.abc.com/fr/book
If you have only English & French content and it isn't hard to implement, I would advice using www.abc.com/fr/livre
The second point. I do not think it is fine to have the same page in different languages about different topics like books and pencils just from user's point of view.
However you can create your pages the way you want and using tags you can tell search engines that www.abc.com/fr/crayon is the French version of the www.abc.com/book page.
You can learn more about the hreflang tags on here.
Regards,