Hello Eva
I have found a workaround for this issue
The solution is based on WordPress plugin named: CategoryTinymce
( https://wordpress.org/plugins/categorytinymce/screenshots/)
After installing this plugin, he extend the capabilities of the category description
For example
Before we use this plugin, the category interface look like:
http://i.imgur.com/hM1NCBq.png
After we use this plugin, the category interface look like:
http://i.imgur.com/LsioGBc.png
and the result is:
http://i.imgur.com/1S11PK3.png
Eyal