"Struth" Is actually an abbreviation of "God's Truth" and is popular elsewhere. Australia, in its isolation, is innocently unaware of such similarities.
Many of the slang terms actually belong to various societies.
The Canadian "Eh" for example (pronounced "A"), is actually part of every day speech in many countries including Australia & even Scotland where the finest English in the world is spoken.
It's a well known fact that the United States would have been named "Amerik" had one of their founding fathers not had a short stay at Niagara Falls on his honeymoon.
A story that has been told and retold until it has become a part of the very fabric of the USA, much like the postal uniform which I wear so proudly today.
Sincerely
Cliff Claven