Complex sentence: When the city of Groningen developed an important position in the Ommelanden, a switch from Frisian to Saxon occurred, although it was not a complete switch because there are many Frisian influences in the "new" Groningen language.
Split into simpler sentences: When the city of Groningen developed a mighty position in the Ommelanden, a switch from Frisian to Saxon occurred. Although it was not a complete switch because there are many Frisian influences in the "new" Groningen language.