The Lalairu are very open to discourse with outsiders, if the outsider can manage to understand the very erratic Lalairu speech patterns. Their language is called Lalairsa, and it was made up of many different languages, making it very hard to translate. (TNG novel: Dark Mirror)
In the late 23rd century, the Lalairu aboard the vessel Mascrar mediated a dispute between the United Federation of Planets and the Romulan Star Empire at RV Trianguli. Unfortunately, the peace talks broke down. (TOS novel: Honor Blade)
In 2366, Starfleet Commander Hwiii, a delphine, traveled with the Lalairu to the Great Rift region to investigate the nature of subspace hyperstring structure. His well-adorned special suit also had the emblem from 20th century NASA. (TNG novel: Dark Mirror)
Lalairu count a person's experience by the number of times one dies, for they have the capability to regenerate after death even if only a single strand of DNA remains. There were problems at the Lalairu's first contact with other races until they were made to understand death was permanent for most species. (TNG novel: Intellivore)
The Lalairu first appeared in Diane Duane's novel Dark Mirror. Years later, she revisited the race in the TNG novel Intellivore, though they were portrayed quite differently. It seems as though Duane forgot the information she had already established about the Lalairu in Dark Mirror, and no editor caught the error. The subsequent Rihannsu novels also featured the species, depicted as they were originally in Dark Mirror.
However, it could be theorized that the Lalairu described in Intellivore could be just one branch of the species-group, though the novel's description seemed to indicate that all Lalairu were the same.