It is well below minimum wage. But you get free food and a free place to stay, right? So you can spend everything on other things. With € 260 per month you will definitely not be rich, but you can afford to go out a little.
"For all au pair contracts signed after 1 July 2013, it is compulsory for German host families to contribute 50 euros a month to the cost of their au pair's language course, provided that the au pair requires a visa (non-EU nationals) or comes from Croatia." (via http://www.aupair-world.net/index.php/au_pair_program/germany/family/pocket_money) - so you get some moneys towards that, too.<br />
I've not seen any mention of getting more than the minimum pocket money. All your expenses are taken care of, like any other member of the family.<br />
Wikipedia says (and other sites confirm) that "The majority of families also give their au pairs a monthly travel pass and other benefits such as a contribution to course fees" and the Au-pair society confirms that they are responsible for at least travel to and from language classes.