# documentação Django 2.0.8

# Código fonte para django.conf.urls.i18n

    import functools

    from django.conf import settings
    from django.urls import LocalePrefixPattern, URLResolver, get_resolver, path
    from django.views.i18n import set_language

    def i18n_patterns(*urls, prefix_default_language=True):
        """
        Add 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)
        return [
            URLResolver(
                LocalePrefixPattern(prefix_default_language=prefix_default_language),
                list(urls),
            )
        ]

    @functools.lru_cache(maxsize=None)
    def is_language_prefix_patterns_used(urlconf):
        """
        Return a tuple of two booleans: (
            `True` if i18n_patterns() (LocalePrefixPattern) 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.pattern, LocalePrefixPattern):
                return True, url_pattern.pattern.prefix_default_language
        return False, False

    urlpatterns = [
        path('setlang/', set_language, name='set_language'),
    ]