Burbank, Glendale, San Fernando, and Calabasas are all independent cities lying within the San Fernando Valley. All others are districts of the city of Los Angeles. Locals refer to the San Fernando Valley simply as "the Valley".
The stereotypical "Valley Girl" speak is actually prevalent among most teenage girls influenced by pop culture all over the USA, and not just limited to the San Fernando Valley. San Fernando Valley residents are diverse with Spanish, Korean, Thai, Armenian, Hebrew, Persian, Russian, Tagalog, Vietnamese, Hindi, and many other languages being common besides English.