can you just have the setup assistant run the country selection?

If the image is just a vanilla 10.10.5 it should go to the setup assistant. If you're using Casper Imaging it will skip that and take you to the login window.

Are you adding anything to the AutoDMG build or running a first boot script after deployment?

Does it look like the imaging process is completing successfully?

Regarding region settings, if none are applied it will use the images default (U.S). I don't think there is a way to just run that part of the setup assistant, although a first boot script or a config profile could configure the setting.

I am not sure if your problem is related to language, but maybe this helps;

There is the file /var/db/.RunLanguageChooserToo
Deleting this file together with the file /var/db/.AppleSetupDone will result in a 'factory' setup assistant that first asks for language, then runs setup assistant.
(see also post of Rob Potvin at macenterprise forum)
I have not worked with this file in 10.10, but I assume it still works the same.
I don't think that just running the language chooser part will work, but you could try....

for scripting: you know the

$ languagesetup -h
WARNING: root access required to change system language
Usage:  languagesetup [-h] | [-Localized|-English] | [-langspec <spec>]
    -h      print this message
    -Localized  print localized prompts (requires UTF8-capable terminal)
    -English    print English prompts (default through 10.3)
    -langspec   specify a language directly (eg. "English" or "ko")

command?

You can modify the Setup Assistant, and remove all the modules that you do not want the user to see, however, in 10.11 you will have some issues so it would be best to convert to DEP now, that will allow you control over what modules show up.

And you need to create the file /var/db/.RunLanguageChooserToo and delete /var/db/.AppleSetupDone to get Language chooser to appear before Setup Assistant.

you could also write a daemon to watch for Language Chooser to quit running, then kill setup assistant. or you could just run

/System/Library/CoreServices/Language Chooser.app/Contents/MacOS/Language Chooser

at any time and just pop it up after a user is logged in.