Also improves handling in cases where account creation did succeed, but
comments service user creation did not.
Depends on commit 88abdd8a0b20bc9816f487b25abdea1953f5661d in https://github.com/edx/cs_comments_service
JIRA: FOR-522
This is necessary to allow non-browser-based services (e.g. notifier)
to know a user's preferred language even if the user has not explicitly
selected one.