Pascal,

That's very easy...
1 - During importation of furniture: highlight the name of a category, and type the new name. That's all.
2 - When using the Furniture Library Editor, it works almost the same: highlight the name and type a new name. The new category is automatically created. If you want to change many category names in one go, first re-order the furniture list, then select all items you want to change, and select Modify.

When there are no items for a category, the category is automatically deleted. Example: when you import English models, the category will be Bathroom. Change all of them to Salle de Bain and the Category Bathroom will disappear.

Hans