Hallo. The key-word in this area are: accessibility (in the technical and content sense) and usability. Anyway, on this website there are international guidelines for accessibility of Web content: www.w3.org/TR/WCAG20/
a good starting point could be the European Directive EN 301 549 V1.1.1 (2014-02) which is open and publicly available at ETSI website (http://www.etsi.org/technologies-clusters/technologies/human-factors?tab=2). There you will find also related standards which may be of interest too.