If you try to load a template named filename.LANG.html it will try to load filename.de.html first, then filename.html afterwards (assuming that German is the currently selected language).
Usage: Put in a file named langtemplateloader.py under your project, and replace django's default filesystem loader with this in the TEMPLATE_LOADERS section of settings.py:
TEMPLATE_LOADERS = (
'myproject.langtemplateloader.load_template_source',
# 'django.template.loaders.filesystem.load_template_source',
'django.template.loaders.app_directories.load_template_source',
'django.template.loaders.eggs.load_template_source',
)