Okay, at first glance here's what I've found beyond the Region thing he mentioned:
1> In your Civilization file, you give your civ Animal Husbandry, but not Agriculture. I doubht that'll cause it to fail outright, but it's probably not a good idea.
2> Also in the Civilization file, you have your list of city names. While none of them obviously jump out as duplicate, you should try to do something unique to make sure there are never conflicts with other mods. For instance, if some other mod also added TXT_KEY_CITY_NAME_MANTLE, and it was loaded before yours was, then your entire file would fail to load. (That's what happens when text keys conflict: the entire file containing the second attempt is thrown out.)
The easy way to avoid this is to name the key something like TXT_KEY_SPATZ_NAME_MANTLE, something unique to your mod. If, by sheer chance, some other mod also uses that city name then you'll see both on the map, which is unfortunate, but that's far less of a problem than a mod failing to load.
3> In your text keys, specifically TXT_KEY_CIV_WYANDOT_TEXT_1, you have an exponent ("40,000 m^2"). I have no idea if Civ5's engine can handle superscripts like that. You should try rephrasing it to "40,000 square meters".
Other than those I didn't see anything obviously wrong, and none of those three should cause it to fail outright, which makes me think that it's more likely a VFS-type issue.
EDIT:
Yep, there's a VFS issue. You have to set "Import into VFS" TRUE for all .dds files, or they won't ever load.