Your system information

• Steam client version (build number or date): steam-launcher 1.0.0.54
• Distribution (e.g. Ubuntu): Linux Mint 18.3 64-bit
• Opted into Steam client beta?: No
• Have you checked for system updates?: Yes

Please describe your issue in as much detail as possible:

Expected:
Open steam with fonts rendering.

Actual:
The console repeats ../vgui_surfacelib/linuxfont.cpp (402) : Assertion Failed: Unable to find font named Arial same for a few other fonts DejaVu Sans, Marlett and Lucidia Console which lead to further errors (read linked log)
These fonts are present in Font Viewer and display correctly.
https://gist.github.com/daerogami/4cbaff7cf2a39e91e0f833b669634d98

Couldn't get a screenshot, but the context menu text from the applets panel in the bottom right is all squares.

Steps for reproducing this issue:

1. Download and install steam
2. Download Segoe UI and manually install the font
3. Force clear the font cache sudo fc-cache -frvE
4. Change {Default Font, Desktop Font, Document Font, Window Title Font} from Noto to Segoe UI
5. Realize it doesnt work and change back to Noto fonts.
6. Install mscorefonts sudo apt-get install ttf-mscorefonts-installer
7. Restart
8. Run steam

This appears to have been an issue as long as steam-for-linux has been around; however, solutions such as upgrading the OS, installing every relevant font under the sun, installing fonts in ~/.fonts, installing fonts in steam's fonts folder have all proved unfruitful. I cant even remember some of the other guides I have attempted. I'm really puzzled how the client isn't able to access fonts that are clearly available to the OS.

Related to #99