You could probably switch the entire encoding from "latin_1" to "unicode_escape". Probably...
If it has any issues with this, you can do it on a case by case basis instead. In Final Frontier Plus adding BUG added the automatic unit naming option which puts the unit type into the name which for the upgraded unit types includes the delta and omega characters that are added to the game font in place of other characters (great people and electrical power, actually - not that it is relevant). These turn out to be way up in the unicode range at 4000-something, I think (maybe 8000-something). So when the worldbuilder saves were made it initially had this problem. In FFP just the relevant writes and reads for the unit names were switched over to "unicode_escape".