In the apps for mobile devices, you get advice for relates articles. In the Dutch article about "misogynie" (misogyny) you're advised to read the articles about "Kalam (Islam)", "Islam" and "Allah". The Dutch OTRS team was contacted by an Islamic female who thought this to be anti-Islamic. As a member of the Gender Gap project group I also find them very anti-Islamofoob and anti-female.
See https://www.mediawiki.org/wiki/Extension:RelatedArticles, it's possible to override these.
Technically, Elasticsearch finds up to 25 "most important" terms, based on term freq in the document compared to term frequency of all articles combined, in a document. It then performs a search for these terms.
For this document the chosen words were:
allah behoed bestat god hat hetzij hoofdstuk islam koran korintier man mann paulus sommig vak ver vorm vrouw wester
This is roughly equivilant to the query: https://nl.wikipedia.org/w/index.php?search=allah+OR+behoed+OR+bestat+OR+god+OR+hat+OR+hetzij+OR+hoofdstuk+OR+islam+OR+koran+OR+korintier+OR+man+OR+mann+OR+paulus+OR+sommig+OR+vak+OR+ver+OR+vorm+OR+vrouw+OR+wester
It's not exactly the same because the morelike search is performed against a single field, the text, while providing the same list of terms to the full text search uses 7 different fields to build up it's score.
Thanks for explaining!
Now: how can I change the chosen words/how are the words chosen? (And by document you mean "article"?)
In web you can override these with {{#related:Preferred title}} {{#related:Preferred title 2 }} {{#related:Preferred title 3}}
@Ciell as mentioned by @Sjoerddebruin you can set a fixed list of recommendations on a specific article by using a special wikitext syntax (please see https://www.mediawiki.org/wiki/Extension:RelatedArticles).
(It's not possible to tune/choose the set of words used by Elasticsearch).