New answers tagged linux
You need Mono installed, and if you are running 64-bit (most likely) you may also need to install the 32-bit versions of the graphics libraries that Mountain needs. Ubuntu has most of these libraries installed by default, but only in 64-bit. This is what I did to get going: sudo apt-get install mono-complete libglu1-mesa:i386 libxcursor1:i386 ...
If you want an addon manager for Linux (also windows and OS X), you may want to check out http://www.wowmatrix.com/.
I found some instructions here: http://steamcommunity.com/app/8930/discussions/0/540744299996631016/ or maybe better is here: http://forums.civfanatics.com/showthread.php?t=528742
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