The Vector Watch app
At this point, the Windows Vector Watch app is available in English, while the iOS and Android version is available in English, French, German and Spanish.
Your Vector Watch app will inherit the language setting from your phone, and default to English.
The notifications you receive
When someone sends you a notification or calls you, you will see it displayed on your watch. The supported languages for notifications and caller IDs are:
VOS (Watch version) v1.0.0
VOS (Watch version) v1.1.0 (and higher)
So messages like "J'y suis arrivé" or "¿Que hora es?" should display just fine.
The Event Name stream
Similar to notifications, event names with special characters will display just fine in the languages supported by the notifications system.
The watch streams, apps & user interface
At this point, for Windows Phones we only support English on the watch, while for Android and iOS we support English, French, German and Spanish.