FedoraBubbles and FedoraDNA gdm themes have strings that are not translated, e.g. "Please enter your username" and others in the xml.in file. Either export the strings to the redhat-artwork POT file for translation, use Bluecurve translations, or, best, not use any custom strings at all and inherit from gdm if possible (like already done for "Shutdown", etc.).
I believe any prompts like "Please enter your username" come from pam, and should not be hardcoded in the xml, but we should check to make sure.
I looked through FedoraDNA.xml.in, and it has no nonempty text elements, except for formatting characters.