I have deployed a Web Apllication with Web AppBuilder developer 1.2. I am using a French OS and just found out that using the developer edition, you have to rename the config file in order for the BaseMap Gallery to work. Under ...\"CustomApp"\configs\BasemapGallery\rename to "config_Bibliothèque de fonds de carte.json". Otherwise the BaseMaps won't be displayed.
Hope this help other "localized" users
Gaz Metro, Montreal