They speak the Pennsylvania Dutch dialect

The Amise have their own dialect: the Pennsylvania Dutch dialect. Of course, the use of Pennsylvania Dutch varies among different Amish communities, and there can be differences in the specific dialects spoken. 

Pennsylvania Dutch is often used in daily conversation, particularly within the Amish community, and is passed down through generations within families.

Still, many Amish communities in the United States, particularly those in Pennsylvania and surrounding areas, speak a dialect known as Pennsylvania Dutch or Pennsylvania German. 

Pennsylvania Dutch is a West Central German dialect, and it is not a form of Dutch but rather a corruption of the word ‘Deutsch,’ meaning German.