My 2 cents of specifications of this feature, very important to provide the best user experience to customers:
In the general settings of the knowlgede base, have the possibility to define one or more languages that will be available when writing and reading articles. Possibility to define a default language in the settings too.
When editing article, have a possibility to choose the language of the content you are editing.
When reading the article, display the content according to the browser language, and if it is not available, display the article in the default language, and also give the possibility to user to choose the language of the article.