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*****a 64bit version has been uploaded to GOG now and fixes the problems
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The new update launch today (10/4) 2.044 breaks compatibility with a LOT of Linux distro's due to the game's binary needing to be link to the systems glibc library version 2.27 or higher, only Ubuntu 18.04/18.10 & Fedora 28 have this listed containing this library by default. All older ubuntu versions 17.10 or Lower, {Current} Debian 9 or Lower,Fedora 27 or Lower, {Current} Open Suse 15 or Lower, will not be able to run the game.

Arch,Gentoo and other Rolling Releases Distros should have the compatible library.

In case some are wondering Libc really can't be updated by itself as most programs in the system depends on the version shipped - and can cause MAJOR system breakage if not done correctly( I do not recommend it).

*Edit: I've submitted the problem to gog support

**Update: After 6 days GOG support basically told me they can't support Debian 9, which my message was about Ubuntu 14.04 & 16.04 support (though you have to send a system diagnosis list which obviously shows me running debian 9); other than that the message was forwarded to the "Linux Team" - so maybe that's good? Idk. I wish there was a general "Report Bug to Devs" features on GOG instead of a list of random items to pick through for gog itself. I checked my steam version and it has the same problems, then I checked taleworld forum and in the linux thread its stated they are aware of the {glibc} problem and are trying to fix it(no time frame stated).

***Update(10-19-18): No news yet on when they're fixing the problem though there is a work around: If you install the older binary (mount_blade_warband_en_1_173_17968) hopefully from a backup and copy over the Module Folder (Native and Napoleonic Wars) from the new releases it will work with the old binary and still allow you to play in online servers without a problem.

****Update(11-1-18): The Beta(test) version on Steam is now working correctly and now includes a 64 bit build(which I hope gets on gog too).

The new Warband update is also broken on ArchLinux due to a missing library.
./mb_warband_linux: error while loading shared libraries: libsndio.so.6.1: cannot open shared object file: No such file or directory
ArchLinux does not package lib32-sndio

At least that one is easy enough to fix. Just rename/delete libSDL2-2.0.so so that your system SDL2 is used (assuming you have a 32-bit system libSDL2).

For gentoo, I also have to install an older GLEW and link curl to the name the game needs.

glibc is pretty standardized as well, so you can probably just add the needed libc from another distro to the game directory to pick up just for that game, without any serious impact on the system.

A quick rm to the included 0-libSDL2-2.0.so.0 and the new version successfully runs. Thank you for your advice. On Arch the prepackaged lib32-glew1.10 and lib32-libcurl-gnutls are required as well.

tried it, I just get a "Segmentation fault". libc is a pain with debian since most system packages are linked to main system one(my case 2.24); gentoo I believe might be compiled differently to allow more swapping of the key system libs given that its a rolling release. It also doesn't help that the game require 32bit libs(it's always been the case with this game but ugh..).

OK, sorry, I was just guessing. It shouldn't have major ABI changes unless there are associated major version number changes, but I don't trust Drepper or the glibc team that much anyway. Of course it could just mean that the libc you used was compiled with different options, or incompatible kernel headers, than the one supplied by your distro. In any case, I'm not even sure how you know it needs 2.27 or above, and I'm too tired lately (I can't even focus well enough to read what I'm writing any more) to investigate further, especially since it doesn't affect me directly. The only thing I can say is that gentoo doesn't do anything special in that regard. Sorry.

It's alright, I would have suggested something similar if I was trying to probe a problem. The reason I know it needs glibc 2.27 is because the binary's fail to launch and the error output reads "version `GLIBC_2.27' not found (required by ./mb_warband_linux)" also ironically this happened to me about 4 years ago, was running an older version of debian(i think 7) and a update for this game required a newer glibc than what my system came with which resulted in me installing a new debian unstable Kernel AND glibc + other packages(I needed them to work together) and well it hard bricked my system lol. My main issue with the update now is the official gog support for ubuntu 16.04 &14.04 will not have these libs in the main repo.
Also a general update:
Gog never responded anything back from what I sent them though I have the game on steam and its a problem on there too and I checked the taleworlds forum and the devs are aware of this(glibc) problem and are trying to fix it.