West Frisian (Westfries) was a language which was spoken in the historical region West Friesland. Not to be confused with the spoken language of the Friesland province internationally indicated with the name West Frisian language (in Dutch simply Fries) although they are related to each other. Therefore the Dutch name Westfries is sometimes used in English.
The language came into life during and after the wars with Holland, around the 12th and 13th century. But from the late 15th and 16th century it became little by little affected by other dialects and languages, such as Brabantic, Hollandic and Dutch Low Saxon. At first the changes where small, some dialect arrived, such as the now still known dialects Zaans and Waterlands and other smaller dialectical differences between speakers. Not much was actually written in these languages or dialects as the region was politically dominated by the Hollandic Dutch-speaking region of Holland.
From the 18th century that effect was also making that the language was slowly developing into a dialect itself and so it was becoming increasingly Hollandic and Dutch. In the 19th century the language itself has almost completely disappeared. Although some say the heavy dialect, the West Frisian dialect (West-Fries) that is, is a continuation of the language. Halfway the 20th century it has also almost completely disappeared. Currently only the strong and light dialect remain; West Frisian, Zaans, Waterlands, and the closely related Kennemerlands and Strand-Hollands outside the historical region of West Friesland.