# documentación de Django - 1.10.7

# Código fuente para django.conf.urls.i18n

    from django.conf import settings
    from django.conf.urls import url
    from django.urls import LocaleRegexURLResolver, get_resolver
    from django.utils import lru_cache
    from django.views.i18n import set_language

    def i18n_patterns(*urls, **kwargs):
        """
        Adds the language code prefix to every URL pattern within this
        function. This may only be used in the root URLconf, not in an included
        URLconf.
        """
        if not settings.USE_I18N:
            return list(urls)
        prefix_default_language = kwargs.pop('prefix_default_language', True)
        assert not kwargs, 'Unexpected kwargs for i18n_patterns(): %s' % kwargs
        return [LocaleRegexURLResolver(list(urls), prefix_default_language=prefix_default_language)]

    @lru_cache.lru_cache(maxsize=None)
    def is_language_prefix_patterns_used(urlconf):
        """
        Return a tuple of two booleans: (
            `True` if LocaleRegexURLResolver` is used in the `urlconf`,
            `True` if the default language should be prefixed
        )
        """
        for url_pattern in get_resolver(urlconf).url_patterns:
            if isinstance(url_pattern, LocaleRegexURLResolver):
                return True, url_pattern.prefix_default_language
        return False, False

    urlpatterns = [
        url(r'^setlang/$', set_language, name='set_language'),
    ]