Another possibility I saw on my Kobo Touch (not sure it works on Aura as well but, why not?!). I've created a "fonts" folder in the root directory of Kobo (when connected through USB, obviously) the I've put the Unifont TTF file you can download from here
http://unifoundry.com/pub/unifont-6....3.20140214.ttf and when reading books in Japanese language (before Rakuten and Japanese firmware), the firmware was able to automagically select such font for symbols that were unknown or unavailable in the font I was using for reading.
I still using this font (by selecting it through the menu) for novels and so on. Obviously technical books with programming languages and things like that are better with "default" one due to normal text, fixed width and so on. But still, Unifont is "the whole" human-readable character set... and it's also free as in GPL! So if you have symbols problems, take a look.
NOTE: the font it's hugely huge (>10MB but contains glyphs for every printable code point in the Unicode 6.3 Basic Multilingual Plane (BMP). The BMP occupies the first 65,536 code points of the Unicode space, denoted as U+0000..U+FFFF.)