thank you for bug reporting with decimals - I'll fix that in the evening. Dessert is a good idea, I'll add this feature, again in the evening - can't get to it any sooner.
Categories - you can display pizza by category using wp-nav menu (you'll have to show category boxes throught screen options in the upper right corner). And again, in the evening I'll add a param to select category into shorcode also.
About the frech translation - cool! You can find a .pot file in a folder /languages of the plugin (of latest version 1.0.4). It's called wp-pizzeria-default.pot - copy that file, rename it to wp-pizzeria-fr_
FR.pot - translate in your favourite software and save it. Than, send me both .pot and .mo file to firstname.lastname@example.org - I'll give you all the credits for french translation on plugin's page ;)