Created attachment 143078 [details]
glxinfo | grep strings

4.20.0-arch1-1-ARCH
mesa 18.3.1-1
steam 1.0.0.59-1
R9 285 (Tonga)

In game menus and other game play elements aren't rendered correctly by
default:
https://imgur.com/a/AvclRkS

There are no special steps required to replicate the issue.

Affects other Linux distributions and other cards:
https://steamcommunity.com/app/10500/discussions/0/1319962244123571976/

A known workaround for the problem is to edit:

~/.local/share/feral-interactive/Empire/preferences

Changing the value of the following line to zero:

<value name="UsePBOSurfaces" type="integer">1</value>

There doesn't appear to be any downside to this.
Medieval 2 Total War doesn't appear to be affected on my setup.
Unable to test Shogun 2 or Fall of the Samurai as I don't have access to those.