Excerpt from change request document:
Southern and Southwestern Nisu were originally grouped together and referred to as Yuanjiang-Mojiang Nisu. However, the lack of mutual intelligibility between these two varieties suggests instead that they should be split into two distinct languages. During 2006, Ken Chan (also with EAG) and Cathryn Yang carried out a dialect survey of Nisu, in which they tested Northern and Southern Nisu speakers if they could understand a Southwestern Nisu RTT. Only one Northern Nisu data point could adequately comprehend (RTT score avg. 80%); all the other N and S Nisu points failed to adequately comprehend SW Nisu (scores below 80%, often 50 or 60%). Also, they tested SW Nisu speakers on how well
they could understand N and S Nisu varieties. The SW Nisu speakers were unable to adequately comprehend any of the other Nisu varieties. SW Nisu is linguistically very closely related to both N and S Nisu, but the speakers moved away from the Northern Nisu area several generations ago to the southwest. Because of the lack of mutual intelligibility with other Nisu languages, Chan and Yang concluded that SW Nisu was a related but divergent Nisu language.Northern Nisu refers to [yiv], currently named Eshan-Xinping Yi (name change requested).