According to Wikipedia:
Salatiga is a city in Central Java, Indonesia and located between the cities of Semarang and Surakarta. It sits at the foot of Mount Merbabu (3,142 m) and Mount Telomoyo, and has a relatively cool climate due to its elevated position.
Salatiga is thought to be named either after the goddess of Trisala, or after the three wrongs done to the first king of Semarang.
In the first explanation, the people of the village celebrate the goddess of Trisala called the village Trisala and in the years to come became Salatri and eventually Salatiga.
The second explanation is based on the story of Ki Ageng Pandanaran, the first regent of Semarang, who was robbed by three muggers, and he thus named the location Salah Telu. Salah means wrong in both Indonesian and Javanese. Telu is Low Javanese for three, as is tiga in both the more refined Middle/High Javanese, and in Indonesian. Hence the name Salatiga from Salah Tiga.