It isn't a redundant phrase - "Extraterritorial" means the same as it
does in English - the "es" is only a grammatical suffix.

Gebiet is not solely "territory" as in a political way except in the
sense of a "place we posses and rule that has dimensions", but more as
an "area" or "grounds", as in "mein Fachgebiet" which is "my area of
expertise". Or, as after the end of WW II, when the British and US
sectors of W. Germany were economically merged and became the
"Vereinigte Wirtschaftsgebiet" a.k.a. "Bi-Zone", where "Gebiet" was
officially translated to mean "Zone" in the German equal of the US
Federal Register (the "Gesetzblatt").

Len