Buttons and labels will normally show in the language users have set in their own browsers.
You can however force a specific language when they load a guideline using a link, by using a language-code in the link. This will only work if they go directly to the guideline using the link.
To make links using a language-forcer, you need to add ?locale=XX in the end of the link, where XX is the language you want to force (e.g no, de, fr, nl..).
This works on links to public guidelines using the guideline shortcode, like this:
It also works on links to evidence summaries, specific recommendations and sections.