How was Switzerland transliterated into Chinese?
Did 瑞 used to be pronounced suì in 官話?

It was pronounced far closer to suì than today’s ruì, and more than enough to warrant the use of 瑞 as a transcription for Switzerland or Sweden.


Excerpt from
元・周德清《中原音韻》,
detailing the phonology of 13th Century Central Plains speech, a.k.a.
Old Mandarin. The
characters 睡, 稅, 說, and 瑞 are pronounced identically. The expected
Mandarin reflex of 瑞 is shuì.

Excerpt from the Ming Dynasty publication 《洪武正韻》, which details the speech of Ming-era Mandarin. The dictionary gives the Fanqie of 瑞 as 殊偽切.

Whatever changed the pronunciation to r- must have happened relatively recently...