You can avoid data traffic when abroad by deactivating data roaming. No connection to the Internet via the mobile network can then be established. You can still use WLAN even though data roaming is deactivated. To activate or deactivate data roaming you need to activate mobile data.
Find "Mobile Network"
Press the Menu key twice.
Press Networks and Connections.
Press Mobile Network.
Activate or deactivate data roaming
Press While Roaming.
Press On or Off.
Return to the Home screen
Press the Return key to end the session and return to the Home screen.