Is it correct that the management company taking care of the property we own can legally reject any type of communication in any language that is not german ? Would english or another national language be admissible (french or italian) by law ?

Just asking because my property manager only accepts emails written in german, so I was wondering if that's legal (I think it is, but just double checking if someone knows better).

Thanks in advance.

Yes a company can specify the language they will correspond in - I'm not sure there's a specific law on this, but if you sign a contract in German the company can expect that to be the language used.

TBH a property manager in Zurich not accepting simple English emails seems a bit surprising and pig headed, but on the other hand if it's not something you need absolute certainty on just stick it through Google Translate or DeepL and problem solved.