Hello,
Yes, the name Roissy (name of the nearby town) is still very widely used in France to designate the airport. I only use the name "Charles de Gaulle" when I am speaking or writing to foreign visitors who might not be familiar with the name Roissy.
In emails or text messages in French, I can use "CDG" rather than "Roissy" (but never orally). CDG1, CDG2...
All the people I know who live in Paris or have lived in Paris say "Roissy", whatever the terminal. The name doesn't change, whether it's terminal 1, 2 or 3.
To prevent confusion, some brochures sometimes say "Roissy Charles de Gaulle" but it's a bit of a mouthful.