To further clarify "preview as", unless you're a GM it's severely limited when using private groups (and languages, which are just a special way of addressing groups).
In a nutshell to avoid revealing members of a private group it'll assume the "worst".
That is if you say "private to group xxx" it'll assume the player is not a member. If you say "private to not group xxx" it'll assume they
are a member.
So, if you preview as "Bob" who is or isn't a member of the private group "Whatever" (the result is the same regardless whether he's a member of the private group):
Private line | Visibility |
---|
Private to Bob | Shown |
Private to group Whatever | Hidden |
Private to not group Whatever | Hidden |
Private to Bob; group Whatever | Shown |
Private to Bob; not group Whatever | Hidden |
Language Whatever | Scrambled |
Also, if you preview as Bob and he doesn't have access to the thread then everything will be hidden/scrambled anyway. Kind of a moot point as they can't even open the thread, but the permission check figures the character has no access to the thread so hides everything. Behaviour of this could be changed and instead provide a theoretical view if they did have access, might be slightly helpful of a GM plans on moving the thread group after (or giving the character access to that group).