In Linker.php we have a line like this:
$magnifyalign = $wgContLang->isRTL() ? 'left' : 'right';
which will result in a "float" style to be added to the magnify icon for images. The above means, the icon will appear to the right on LTR wikis. That "is" a problem for wikis like Meta or Wikimediafoundation where the wiki is generally LTR but has some RTL pages on it too.
If there is no objection, I'm going to modify that part and let Common.css to define the float of such objects. That way, CSS hacks can be used to move the icon to left/right as desired, and the option is in the hand of Wiki admins, not hardcoded.