The Reason ONE is currently only sold in the United States and capable of using American English. However, if you have a US Amazon account and are comfortable with using English, you can take the Reason ONE to Europe and use it normally.
For the Reason ONE clock to work, you will need a US Amazon account and Internet access. Regardless of your geographic location, the clock will operate normally.
To change the time zone, you will need to go into the Reason Home app and Amazon Alexa app. In the Reason Home app, tap the tile of your clock, tap the Settings gear symbol, and tap Time Zone. In Time Zone, you can adjust the country and specific time zone you wish to use. In the Amazon Alexa app, go to Settings, tap Device Settings, tap the Reason ONE clock device, and then go to Time Zone. Under Time Zone, you can change the country and specific time zone.