Rubidium opened the ticket and wrote:

When starting OpenTTD and it finds a misc setting that is invalid, i.e. triggering ShowErrorMessage, OpenTTD crashes nastily due to missing language files.

Adding an initial language initialisation before loading the minimum part of the config does not solve the issue as now the sprites aren't loaded. However, the sprites shoud only be loaded after we know which set to use, ... So all-in-all there needs to be some method for postponing the ShowErrorMessages from very early startup.

If language/blitter/videodriver are invalid this will yield another type of error and for the rest OpenTTD can work on the default values as well until we are far enough in the start procedures to show the error messages.

Reported version: 1.2.0-RC4
Operating system: All

This issue was imported from FlySpray: https://bugs.openttd.org/task/5154