The notice was circulated on social media with many students expressing their outrage, with some comments saying it was “dictatorial” and “completely the wrong approach”.
The rule also applies to breaks between classes and even to telephone conversations students have with their parents - if they are within earshot of other students.
An exception is made for language classes taught in English, Spanish, French and Italian.
The head of the school management board, Martin Göbel, told the Austria Press Agency that the note was “ambiguous” and not “very well formulated” but confirmed that it was genuine.
Göbel said that the reason behind the foreign language ban was a fight between an ethnic Albanian student and a Macedonian cleaner, who is employed by the school.
The pair had started arguing and in the ensuing row a Turkish-speaking student felt that she had been insulted and reported the incident to the school principal. “The headmistress felt that this presented an opportunity to remind everyone that German is the official language of the school,” Göbel said.
He said the announcement was not actually a ban but was aimed at raising awareness about how "language confusion" could lead to misunderstandings.
He added that students could continue to speak to each other in any language they pleased outside of the classroom, and said that there was no problem with cultural cohesion in the school.
A copy of the notice. (Facebook screenshot)