Which Mongolian languages have a high degree of mutual intelligibility?

With the exception of outlying languages such as Moghol, Daur, and Monguor, the central Mongolian languages share a relatively high degree of mutual intelligibility.1

The central group includes the western languages—Oirat and Kalmyk—and the eastern languages, which consist of Buryat and Mongol (including the dialects of Inner Mongolia and Khalkha). While these languages are historically divided into eastern and western groups, they share many linguistic features, and the spoken dialects of Khalkha, Buryat, and Mongol in China are considered to be little differentiated. Similarly, spoken Oirat and Kalmyk are very similar to one another.213

It is important to note that while the spoken forms are closely related, the written languages often exhibit greater differences due to divergent spelling conventions, distinct political histories, and variations in vocabulary.13