The West Frisian language is spoken in the Dutch province of
Frisia and in a small part of the province of Groningen.
The East Frisian language was common in East Frisia, Germany,
but is nowadays only spoken by a small population of Saterland, a
municipality in the district of Cloppenburg, Germany. Since
Saterland Frisian is the only remaining dialect of the East Frisian
language, Saterland Frisian is often seen as a langauge itself, or
its name is given to the entire East Frisian language.
The North Frisian langauge is spoken in the district of North
Frisia, Germany, and Helgoland, Germany. The language consists of
two groups of dialects and not all dialects are mutually
intelligible with each other.
The three Frisian languages are not mutually intelligible to
each other, but native speakers shouldn't have much difficulties
learning one of the other Frisian languages.