WhatsApp uses the default language enabled on your phone. If you change the language of your phone to English, WhatsApp should be in English. We do not yet have an option to change the language of WhatsApp without changing the language on your phone.
If you are uncertain about how to change your phone's language, please consult your phone manufacturer's user guide to change the language on your phone.
WhatsApp is available in over 20 languages. If, however, WhatsApp is not yet available in your language, please check back soon! We are actively working on including additional languages in future versions. You can also contribute translations on our WhatsApp translation website: http://translate.whatsapp.com.