Step1: Rename existing category with the following format

From Knowledge Base admin panel edit category name to the following multi-lingual format

@{appname.section.name|Display Name}

for knowledge base we suggest to put

@{kbase.cat.name|DisplayName}

here is an example for a category name "Office"

Step 2 Adding Localisation Key

Navigate to Admin > System > Localisation

Under Your changes click on Core Apps...

Right click to add new phrase

Enter the translation, here is an example

Click Save button at the bottom of the list page and close the window once you're done.

Step 3 Test!

Navigate back to the Knowledge Base application to check the category name and try changing your settings to different language.