Display of text in aftermarket.pl works fine on Debian 7.5.
Tested with webpage switched to polish and Opera's user interfacer polish.
The webpage uses Source Sans Pro as font, not a webfont!
You have a problem with the display of your sans-serif fonts or with the correct fonts substitution of your Linux.
Please check this in Shell with fc-list:
~ fc-match "Source Sans Pro"
DejaVuSans.ttf: "DejaVu Sans" "Book"