Asserts are always shown with a popup.
The external code is in the .exe file. The XML processing code is always a nightmare to work with, because half of it is not accessible. From my experience, your error message could indeed be related to any problem with opening either the XML file, or even the associated Schema.
If you're motivated to do some more testing, here's some questions/suggestions:
- Just to be sure: have you double-checked that the mod was installed correctly? Not sure what if the installer works with wine, but the archive should
- What exactly happens when starting the game? You get the two error messages, then the program crashes?
- Can you upload the contents of your log folder? ("<home>/Documents/My Games/Beyond the Sword/Logs/" for me)
- Could you try deleting the file
More Naval AI/Assets/XML/GameInfo/CIV4GameInfoSchema.xml? This will cause a bunch more errors that will probably crash the game again; but, we'll see if the game is now able to at least load the two files from your error messages.
- You could also try deleting
GameInfo/CIV4PlayerOptionInfos.xml. I doubt this file is the problem, since the other file (GraphicOptionInfos) isn't changed in either vanilla FfH or MNAI, and still shows an error.
- If all this doesn't help, please try an older version of MNAI (https://forums.civfanatics.com/resources/more-naval-ai-ffh-mod.14499/history). If they work, the problem could be with my compilation process.