Two studies that suggest
“no matter how similar two languages are, and whether you only use them for speaking or writing: if you can use more than one language in everyday life and you are comfortable in expressing yourself in these languages, they do not hamper your achievements and, rather, they seem to represent a precious mental training”.
Commonly, when thinking about bilingualism our first thought goes to people who grew up in a family speaking more than one standard language… But how about the case of people who use both a standard language, such as English or Italian, as well as a local dialect?
Norway’s challenging geography, with a long coastline cut by deep fjords, and an inland pocked by rugged mountains and numerous glaciers, has made it a great incubator for the development of many different dialects over the centuries. Indeed, there is so much variation in the Norwegian language that it features two distinct written versions, Bokmål (the majority variety) and Nynorsk (the minority variety).
Update: Another study
The ability of children to speak any two dialects — two closely related varieties of the same language — may confer the same cognitive advantages as those reported for multilingual children who speak two or more substantially different languages (such as English and French).
Update: Another study here, you don’t even have to speak a dialect!
Bi-dialectalism boosts memory as much as speaking another language Experts say the extra stimulation leads to increased cognitive performance Second study also shows learning a second language can boost alertness The benefits of speaking more than one language have long been debated – with some experts claiming it gives the brain a boost, while others describing it as a distraction.