These aren't a "language" they're called entoptics or phosphenes. Calling this a language is like the other posts here, is pseudoscience.

Entoptics are actual neural gradient patterns of the retina and occipital externalized, from altered states, light-deprivation, trances even extreme expression.

Entoptics are well enough researched (Lewis-Williams, Entoptics: The Signs of All Times) that any New Scientist writer should have at least mentioned this.