Question about Samsung Galaxy S8+ Duos

Just last week came back from philippines and I had no issues in there or in turkey

BTW, you can always extract this kind of information from the model number "SM-G955**F**ZKDAUT". i.e.

SM - Samsung Mobile
G - Galaxy
955 - Model Number
F - Type/variant of the model (F always stands for unlocked 4G/LTE phone)
ZKD - Software build letters usually for PDA (not so important for regular users)
AUT - CSC code for Switzerland (this usually means that phone has been optimized and tested for Swiss carriers but not limited to...)

If you have ever flashed official software manually you would noticed that CSC file comes separately, this is because it stores all the important information from various carriers, network configs and etc.

Hope this helps in future!
Cheers

It definitely works in EU, haven't tried it outside Europe yet.