Possible solutions are, but not limited to:

• use the HTTP header settings as given by the browser (which would mean that the language is actually switched in the browser chrome)
• use the babel boxes from the user pages (as Wikidata, several disadvantages, don't exist for logged out users, hard to discover, expensive)
• extend user preferences and use the values from there
• use different URLs for different languages (e.g. wikifunctions.org/en vs wikifunctions.org/hr or en.wikifunction.org vs hr.wikifunctions.org)

These have different advantages and disadvantages and are also not mutually exclusive. We should decide on which one to use and implement them.