Custom Default Locale on Startup

[Eduard]

Hey,

for a custom Chromium OS build, I am looking for a way to initialize an image
with a different default language ("de"). I don't want to start the image and
then set it manually in the UI.

Is there a way for that, without touching the source code?

My current workflow for the customization is to directly manipulate the
(writable) rootfs partitition from the image via kpartx/mount, which is alright
for my use case.

What I tried:

- Checked Chrome Policies, but the only interesting policy ("ApplicationLocaleValue")
  is not supported on Chromium OS.

- Added a Local State file to /home/chronos/ on both partitions, rootfs and state.
  But that probably doesn't work because the "live" data is encrypted and gets
  mounted and unmounted over my files.

- Added a master_preferences file to /opt/google/chrome/ with the content
  {"intl" : { "app_locale" : "de" } }. (Long shot, I am not even sure if I'm
  using the file correctly)
 
No success at all. What other options do I have?