The opposite of "British thing people in Germany love but few in UK have heard of" would be "German thing people in country X love but few in Germany have heard of".
"The Sound of Music" doesn't really count as an example of the opposite, because it is more of an American thing than a German or Austrian thing. It is an English-language 1965 American musical film, based on an English-language 1959 American stage musical, based on an English-language book written and published in America by an Austrian-American woman. Despite the Austrian setting, and parts of the film being filmed in Austria (the remainder was filmed in LA), on the whole it is more American than Austrian.
There were two West German films made based on the same book, Die Trapp-Familie (1956) and Die Trapp-Familie in Amerika (1958), and the creators of the 1959 American musical got their initial inspiration for the project from watching those West German films. Still that doesn't change the fact that the American musical and American film are American not German or Austrian. And I'm not sure how much of the actual content of the American musical and film are due to those West German films, as opposed to them merely being a motivator for the musical's creation.
The opposite of "British thing people in Germany love but few in UK have heard of" would be "German thing people in country X love but few in Germany have heard of".
"The Sound of Music" doesn't really count as an example of the opposite, because it is more of an American thing than a German or Austrian thing. It is an English-language 1965 American musical film, based on an English-language 1959 American stage musical, based on an English-language book written and published in America by an Austrian-American woman. Despite the Austrian setting, and parts of the film being filmed in Austria (the remainder was filmed in LA), on the whole it is more American than Austrian.
There were two West German films made based on the same book, Die Trapp-Familie (1956) and Die Trapp-Familie in Amerika (1958), and the creators of the 1959 American musical got their initial inspiration for the project from watching those West German films. Still that doesn't change the fact that the American musical and American film are American not German or Austrian. And I'm not sure how much of the actual content of the American musical and film are due to those West German films, as opposed to them merely being a motivator for the musical's creation.