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.
Find "mobile network"
Slide your finger left on the display.
Press mobile network.
Activate or deactivate data roaming
Press the field below "Data roaming options".
Press roam or don't roam.
Return to the Home screen
Press the Home key to end the session and return to the Home screen.