What the hell are you doing with acars messages, that aren't intended to be received by an outsider?
Nothing personal, but this reminds me to not send company-sensative messages through acars.
And to answer your question. The acars we send from ops here in amsterdam are normally plain language. And if you sometimes can't understand what it says, it could be because it is something typical for that flight, but the dispatcher knows what to do with it. Sometimes I don't understand an acars for a collegue of mine, if I don't know what was going on with that particular flight. Besides, we normally send it in dutch. Looks like encrypted language to you maybe
Oh, and we receive it on plain paper on a printer, if that's what you mean..