They use it similarly in "Han laver en scene." / "He is making a scene." Might just be used idiomatically.
the pronunciation is really off In normal speed I, as a dane, couldn't hear "derinde", I heard is as "dagen" In slow speed "laver" was pronounced like "larver"
It is, but only lawyers use the word "therein", and only with other lawyers.
I can't quite distinguish the pronunciation of derinde and derhenne. I thought I heard the almost mute H but apparently it wasn't there.
Poor translation. In English, you can never say "in here" or "in there" as long as you don't want to murder the language.