I use language icons to allow the user to navigate to a page in another language. The language icons are all made equal size by using the width and height attribute. For img tags, this is an accepted, not deprecated, attribute.

However, your img { height: auto; } declaration (arctica.base.css, line 86) overrules the height attribute, preventing the language icons from displaying as intended. Unfortunately, this setting cannot be undone, so there's no real solution this problem other then removing this declaration from your css.

Apparently, your assumption is that all images are responsive, which looks IMO not correct. I guess that even in a responsive design, I can opt e.g. for thumbnails to be fixed size and let them flow over multiple lines depending on the available width. So my suggestion is to remove this declaration or make it apply only to some images by adding a class selector or by using the not pseudo selector:
img:not([height]) (should be working in most browsers: http://www.quirksmode.org/css/contents.html#CSS3, tested personally in FF and Chrome).