Oh I agree that we disagree on the subject.
I will whole heartily agree that the game mechanics in every game I've dealt with for inter-species communications is way over simplified and fast.
What I will disagree with is that communication with a non-terrestrial species is impossible. We have no baseline to make such a universal statement.
The lack of Terran inter-species communication isn't really a valid argument. There is some level of communication with higher level primates (ex. chimpanzees, gorilla's) using sign. The real roadblock is that there doesn't appear to be any other species on this planet that actively uses language for conveying complex ideas. Neither primates nor cetaceans (much less canines) have any appearance of social groups above hunter/gatherer much less a species level of language for complex idea exchange.
But, and this is a big one, if we encounter a species that has risen above hunter/gatherer subsistence there is a chance that communication is possible. The higher the rise the greater the chance. The more things the two have in common the higher the chance grows (ex vocal language y/n, overlapping vocal range y/n, overlapping visual spectrum y/n, written language y/n, etc etc etc)
There is a huge caveat here. Both species must be working together to find the common ground, if it is one sided it is most likely hopeless.
In the case of the Nemotians I highly doubt, under the campaign constraints, that communication is possible. Extremely different interpersonal means of communication. Open warfare. No cooperative effort to find a means to communicate.