So, now I finally found a plugin that allows me to create bilingual articles. In the future I will, if possible, create posts in english too. You can select the language via the drop-down list in the right column.
This article is possibly outdated. It mentions an older version of a software or tool. I haven't checked if the links are still working!
IBM sold their collaboration tools portfolio to HCL Software in 2019, so the product names changed and most of the IBM links are no longer working.