How about an extremely alien speech file, where the Messages are unintelligible?
Say, a good imitation of Shadow chittering, Tamaran metaphoric speech, or maybe a bunch of static from the Arachnids (i.e., Bugs) from
In Death Ground?
Hmm.... bugs. Wonder if there can be a 'devour population' advanced characteristic for when you invade a planet?
(Penalty: pretty much anyone will try to destroy you.)
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"What do -you- want?" "I'd like to live -just- long enough to be there when they cut off your head and stick it on a pike as a warning to the next ten generations that some favors come with too high a price. I would look up into your lifeless eyes and wave like this..." *waggle* "...can you and your associates arrange that for me, Mr. Morden?"