Swedish has du (singular) and ni (plural). Prior to the "du-reform" in the late 1960's however, ni was also used as a formal singular form, but for the last 40 or so years the formal form has been dropped, leaving ni for plural only. In fact many older people would find it mildly insulting to be addressed singular ni today.

Of course there are a few exceptions, most notably when addressing members of the royal family. If you ever get to speak with one of them, the correct way is to address them by title, in third person ("would her majesty like fries with that?").

Around 8 or 10 years ago I started to notice a trend, particularly among younger people (in their late teens maybe), typically working in shops and cafes, who started once again to use singular ni with customers, but I haven't lived in Sweden for several years now and don't know if that's continued. I hope not!