languages in-game
CaptainHellrazor, are you trying to send an entirely private message specifically just to the members of a language group? So that only they can read it? (That's how I'm reading this so far, just skimming, but it's pre coffee so I might be wrong.)
If you're the GM, you can do that as a PM if you want, but yes - as you figured out, you'll have to manually select the members of the group. As a player, you can't do that at all because (and this is the important bit) the code is specifically set up so that players can never tell who has access to what languages.
If, as GM, you wanted to create a group - not a Language Group, but an actual Thread Group - for everyone who spoke Elvish (for instance) so that you can make non-PM posts to them, you can do that. Put all the players that speak Elvish into Group E, and then you can make a thread with posts to that group (by selecting 'E' for where the post goes to) that only they can see. Downside is, they will be able to see who else is in that group, so if it's important to you that players not know who understands the same languages they do, that's a bad option.
Alternatively, you can always make a public post, include a header of something like 'Elvish' (to cover the public part of the post), and then fill in with whatever it is that you only want the Elvish Language Group members to see, either publicly scrambled (by using the 'the Language Group Elvish' option) or completely hidden (by using the 'Private to Group Elvish' option). This is the only way to do it that keeps other people that speak Elvish from knowing who else can speak Elvish, if that's important.
It's worth noting that you cannot use Language Group lines inside of PMs. They won't work, at all. The options aren't even there on the drop-down.