Yep, Budgie is correct. You have a problem with your LANG file. For one, make sure that anywhere it has zoopedia_codename in any file you must rename it to the codename in lower case. This happens once in the entities/units/animals/ai/codename file, once in the ui/zoopedia/entries file, and twice in the lang/1033 file.
Also, you should use a lang file from a user made animal as a template. You can use one of mine if you need a reference. Remember that the files for the animals changed with each XP, and so it might be easier to just see a user made one - the one from APE II is NOT correct.