#(I mean hey its canon that Non-Skaven slaves can pick up on Queekish over time!)

[serpentofslaanesh]

Lyss is naturally fluent in The Dark Tongue, the language of Chaos, but she is also fluent in Queekish, the bastardization spoken by Skaven. Her Slaaneshi nature means that the inherent repetition and quick manner of the Skaven tongue is no trouble for her to replicate.

That being said, Lyss doesn't actually speak it much herself unless she has shapeshifted and needs to blend in, or under other select circumstances.