A Swedish fencing master & physiologist named Per Henrik Ling, created a form of massage based on physiology. It was called Swedish massage later on by various European therapists who worked with his methods since it was developed there. It probably sounded better than saying Ling Massage. This was in 1812.
Esalen Institute is located in California. They extended some of the basic Swedish massage techniques utilizing the entire body, during the massage. Europeans usually refer to Esalen techniques as a California massage, since it was developed here.
The Esalen Institute really worked to bring massage into the human development/awareness movement, recognizing that there were psychological benefits to be gained from massage as well as physiological.
So basically Swedish massage means long relaxing strokes on the body and Esalen means treating the entire body as a whole during the massage.