It might help if we knew about your desktop environment --KDE??
I know WINE installs Microsoft fonts, and maybe, since Netflix uses the web browser,
those fonts are getting mixed in somehow. I would start from the basics and have a look
at this great page by LQ member DuganChen http://duganchen.ca/writings/slackware/fonts/
Configuring fonts in any Linux can be quite hairy since there are about 10,000 ways to do it.
Another thing that makes it tricky is that WINE is not part of Slackware proper.
Are you sure you installed fontforge and webcore-fonts? It seems from your 1st post that you
did not install WINE first but wine stuff came in with Netflix player.
I would start with a proper Slackbuild of WINE in place and then
add in the netflix afterwards.