In windows we all generally use english which is the main language of windows. You can also install new languages into windows which will make using the computer interesting.
You can try it without fear cause there is also an option to uninstall languages, which can be hard to find if you install a language if you dont know. There are plenty of languages available for windows. After choosing a language verify that it is the language you are looking for cause if you install a language you dont know you may be in some trouble. To install languages, in the search box type "Install or uninstall display languages" and select the option.
Click install display languages to install more and uninstall display languages to uninstall languages which is not a good option. You can get languages through windows update or download them manually from the net which is a better choice. Now if you have downloaded the file then select browse button and select the language file. 
Uninstalling is also easy, just select the language to uninstall from the given list. Now explore your new installed language.