Complex sentence: Historical perceptual dialectology allows linguists to examine how and why dialects in the past gained popularity; and linguists gain the chance to examine how the perceptual dialectology of certain dialects of languages have evolved a given time.
Split into simpler sentences: Historical perceptual dialectology allows linguists to examine how and why dialects in the past gained popularity. Linguists gain the chance to examine how the perceptual dialectology of certain dialects of languages have evolved over a given time.