MediaWiki + Translate offer great possibilities for creating multilingual sites. However, when it comes to render content they still push anonymous users to English versions in their landing and every click.
If an anonymous user lands in i.e. https://www.mediawiki.org/wiki/How_to_contribute with a browser that has i.e. German as default language, the page shown by default should be https://www.mediawiki.org/wiki/How_to_contribute/de, not the default English version.
It can be that users with their browser in language X still prefer to read content in language Y. If they select another language in the language box, then they should be offered pages in that language when available, in that session or may as long as a cookie can provide the information about this user's choice.