Comment 12 for bug 1709729

I *finally* found the issue I had in mind all along (damn you Launchpad search!):
I'd bet you're facing the same issue we already had in bug #1697681!

Could you check if you have the environment variable "FONTCONFIG_FILE" set? It likely points to a non-existent or invalid "fonts.conf" file.
Delete that environment variable and the issue should be solved!