There used to be special handling of the user card position for RTL locales: https://github.com/discourse/discourse/blob/4896a7dec79203cd44265bb2372c2b4a223c3d26/app/assets/javascripts/discourse/views/user-card.js.es6#L86-L120
With the updates to the user card, that seems to have been removed. The left position in the user card’s inline styles is wrong for RTL locales. From memory, I think the easiest way to deal with it is to set a right position for the user card when an RTL locale is used. The left and right properties can’t just be switched in the inline style rule though.