As I understand it, we would like to request postings in English please, as it is the lingua franca of the forum.
There is nothing in the rules you sign up which says English is mandatory, however, to protect the website and enable the moderators to monitor posts for compliance, then it is an informal rule. Exceptionally, where we have a moderator who speaks the language, we will allow non English posts, as can be seen on other parts of the website. In the case of Hungarian, we don't currently have this luxury.
We don't mind if you post in BOTH languages, if that helps.
Regards
PPRuNe Mod Team.