On a small number of Linux machines it is possible that the levels are loaded incorrectly, while the rest of the game works properly. If that's the case, there are two equivalent solutions:

* launch the game directly from command line with:

LC_ALL=C ./Orbital\ X.x86 (for x86)
LC_ALL=C ./Orbital\ X.x86_64 (for x64)

* add a custom launch option to steam as follows:

LC_ALL=C %command%