[member="Andorreth Vikar"]
In old canon, the primary form of communication is through nonverbal means, primarily body language. The reason for this peculiar development was that the fact Echani are similar in physical appearance (likely due to their origins as a science experiment by the Arkanians), family members being almost indistinguishable more often than not. They then became masters at reading thoughts and emotions through body language and microexpressions.
Consequently, they excelled in martial arts and they came to see combat as the purest form of expression. ("Actions speak louder than words" and all that jazz.) In stressful situations, a person's true character is more likely to be revealed as they're put under pressure, and there are few more stressful events than combat.
I've seen above people mentioning using their own made-up languages for verbal communication, and that's cool, you do you. That said, it's probably Basic for these reasons.
- A near-human race with artificial origins through bioengineering.
- Eshan's relatively close proximity to the Galactic Core, and steady contact with galactic civilization as whole thanks to FTL communication and travel.
- The Echani finding non-verbal communication more efficient than spoken word, which meant that they probably wouldn't invest in going through all the work of making a new verbal language.
I'm sure the Echani have developed their own local dialect of Basic to better suit their culture. I like to imagine most Echani coming off as direct and even somewhat robotic in speech to non-Echani, because I don't see many Echani in making much use in variations of tone (which is a big part of Basic/English) and then the non-Echani on the other side probably can't understand the subtle nuances of their body language which would provide helpful context.
(BTW, I was speaking Sith.)