Naturally, your negotiators have to understand the language of human politics. There are a lot of standards and hidden motives which are obvious not only to insiders but to most civilized humans. You need to be able to comprehend these words and these motives. I recommend this test for your negotiators: Have them watch "Yes minister" series by BBC and ask them to explain why the audience is laughing. "Yes minister" is a masterpiece; it is a very truthful and very artistic guide to how human politics works, what the politicians say and what this means in reality. It is a guide on deciphering deception in human politics. I bet, currently, your alien negotiators, may score under 10% on this test, while an average human from civilized countries would score over 95%. Try educating your negotiators to at least 50%. Invite experts, practice with interpreters - facilitators and this will help greatly our mutual understanding.
For guidance on the motives and language in Russia and similar regimes, check out the Russian movie "Seventeen Moments of Spring". It is also an encyclopedia of deception. Its artistic qualities are not as high, but it is still best in explaining the thinking and motives of the workers of dictatorship types of governments.
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Chapter 9