Inter-Speak is the abbreviated phrase for the interplanetary language developed for space travellers to communicate with those of other species.
Inter-Speak is based on the ancient first language of the universe, otherwise known as "First-Speak". When it was discovered that several species were visited upon by the first beings in the universe, they were able to use that as the basis for communication. Thus a new language was developed that allowed common communication.
As cosmic travellers, Kheldians are fluent in this language, and will often converse with each other in this language.
The exiled alien Qwa is also fluent in Inter-Speak.
As revealed in both "Guardians of the Dawn GRADUATION" and "Furia and the Guardians", Galatea Powers is also fluent in Inter-Speak. It is presumed that her alternate-future version is fluent in this as well.