Followup task from WikiCon 2016.
Could not find an existing task about this; T42379 looks only slightly related.
**Steps to reproduce:**
1. A German-speaking user registered on German de.wp on September 5th 2016.
**Actual outcome:**
1. The user received a confirmation message in English language.
2. The user was very irritated and wondered what the email is about. ("Do they want me to pay something?")
**Expected outcome:**
The email is in German language as the user registered on German Wikipedia.
**Text of message (edited for privacy):**
> Someone, probably you, from IP address 12.345.678.90,
> has registered an account "Abcdefgh1" with this email address on Wikipedia.
> To confirm that this account really does belong to you and activate
> email features on Wikipedia, open this link in your browser:
> https://de.wikipedia.org/wiki/Special:ConfirmEmail/1234567890abcdef
> If you did *not* register the account, follow this link
> to cancel the email address confirmation:
> https://de.wikipedia.org/wiki/Special:InvalidateEmail/1234567890abcdef
> This confirmation code will expire at 21:18, 12 September 2016.