The sections of your site are named automatically. Which also corresponds to the same name you find in the menu.
If you didn't change any name and you decide to switch language, it will automatically modify both the section names and the menu items.
To change the name of a single section, go to Site Editor area and click on the text to edit.
Change the names in the menu
To change the names of the sections in the menu just access the Site Editor area, click on Sections located on the navigation bar. From there by selecting the pencil icon above each name in the menu you can change the names in the menu.