I have jumpseated on both UA and DL from numerous countries and only once have I had a problem. It was out of MXP and AF was working the flight. They were puzzled by the fact that I wanted to ride for "free without a ticket." More explaining and a check with a manager cleared the air on that trip.

I don't anticipate you encountering any problems asking for the Jumpseat on the return, especially since you are traveling out of an English speaking country.