Is it lawful to release under a FOSS license the source code of a game that runs on a collection of game asset files (script files, audio files, sprites, etc.) which is published under a license incongruous for software (for example the various Creative Commons licenses)? Are there any incompatibilities between these two categories of licenses one should be informed about?
I’m not a layer so take my word with a grain of salt, but I think scripts are just code so the CC-licenses are probably not suitable for that.
There are many different FOSS licenses and many different CC-licenses so you probably need to look at the licenses involved to know what is allowed. Not all FOSS licenses are compatible. The GNU GPL says you must release “the entire work, as a whole, under this License” (or a compatible license). If you ask me I would consider the game assets and the game code to be part of the same “work” but, as I said, I’m not a lawyer so I don’t really know. Also note that some CC licenses, like CC BY-NC-ND, are quite restrictive.