Actually for the gnolls and flinds this dnd 5e gnoll was a language. This language was few times spoken like a second language by the bugbears, elves (of the Chondalwood, the Forest of Lethyr, and the High Forest), goblins, lizardfolk, orcs, or half-orcs.
Probably, this language was common like a language in the Anauroch, Dambrath, Lapaliiya, the Shaar, Thay, and Thesk. Gnomes of the Great Dale and halflings of Channath, the Chondalwood and even Luiren also occasionally spoke this language.
Usually, the gnoll language does not have a true script or else a written form, but of course some of the gnolls were shrewd enough for writing in Abyssal.
These gnolls were believed about their language was a special gift to them from the Yeenoghu. Some of these scholars were found so many connections in a gnoll with a Abyssal language to the lend evidence for the theory which gnolls had the demonic bloodlines.
This language was influenced by the abyssal and spoken by the gnolls.