1. Speech
Cassian speech patterns stratify drastically between highborn and lowborn. The highborn tend to speak with a touch of formality and a continental flair, favoring long forms to contractions. They respect the social hierarchy and have a tendency to condescend to those they perceive as beneath their station.
Lowborn Cassian speech, on the other hand, has more in common with a working class British or cockney accent. They're usually direct and to the point, and any embellishments typically take the form of a quick curse or colloquialism.
Source: Loremageddon2. Common exclamations
Cassians often swear by religious terms, "By the Scions!" Also, loss of light or sight, "Shadows and darkness!" "Blind me!"
Lowborn Cassians are similar to highborn, but earthier/more vulgar. "By the gods!" "Scions take me!" "Bloody hell!" "Bollocks!"
Source: Twitter