With the technician on premise you might use google translate.

 

In a phone call... either hope that the technician has a minimum level of English knowledge/is willing to use it.

Or be at home and once the call comes in, do state "Ich bin daheim"

Hello @ulku,

 

you have already entered your customer number in the profile data here, so I made a remark for the technician that you're speaking English. Then it shouldn't be a surprise. 

 

Please make sure that the technician gets access to the room (normally in the cellar) where the phone lines of the apartments come together.  

 

Kind regards Inga Kristina J.