config.add_translation_dirs('colander:locale')

def main(global_config, **settings):
    """ This function returns a Pyramid WSGI application.
    """
    ...
    config.set_locale_negotiator('myproject.locale_negotiator')
    ...
    return config.make_wsgi_app()

def locale_negotiator(request):
    settings = request.registry.settings
    available = settings['pyramid.available_languages'].split()
    return request.accept_language.best_match(available)

[app:myproject]
use = egg:myproject
 ...
pyramid.default_locale_name = en
pyramid.available_languages = en ru