Most of the locals in Rio de Janeiro speak Portuguese. Therefore, it is helpful to have some basic knowledge of the language, especially when dealing with cab drivers, shopkeepers, and street vendors. However, English is also spoken and understood in many tourist areas, so with the help of a translation app, you can get by with minimal knowledge of Portuguese. It's always a good idea to take a map or use a GPS, especially if you plan to move outside the main tourist areas.