Today, the URL of a QRcode is langcode.qrwp.org/Article_name
This should be complemented with a new default like d.qrwp.org/EntityID
This code should get the language links from Wikidata directly and provides backwards compability.
There is one obvious advantage with this, stability. If the article is moved on the originating Wikipedia and a new one is taking its place, the QR-code will point to a completely wrong article. (Probably a Template:For will be put in the top of that article, but that might not be true for other languages.)
A disadvantage is that you always need to make a lookup to see what languages are available instead of heading of to the article directly if the originating article is in the same language as your phone.
So if the $requested_language resolves to 'd' a separate piece of code is run where the call for language would then be something like https://www.wikidata.org/w/api.php?action=wbgetentities&props=sitelinks%2Furls&ids=$request
This returns all sitelinks, and perhaps (or not) you would want to remove all non-wikipedias.
T72159: Forward according to user's preferred language on Special:GoToLinkedPage