Here are the essential steps:
- Install the "Content Internationalization" plugin in Administration / Extensions.
- Go to Administration / Configuration / Content Internationalization.
- Set there root category codes where you want to apply i18n, e.g. "articles, news".
- Set there locales it will be translated into (the first locale is the main one), e.g.:
en|English
nl|Nederlands
de|Deutsch
- Go to Administration / Structure / Pages / Structure Internationalization and translate category names and...