WhatsApp is available in over 40 languages on iPhone and up to 60 on Android. WhatsApp follows the language of your phone. For example, if you change the language of your phone to Spanish, WhatsApp will automatically be in Spanish.
Android: Go to your phone's Settings > System > Languages & input > Languages. Tap and hold a language to move it at the top, or tap Add a language
iPhone: Go to iPhone Settings > General > Language & Region > iPhone Language. Select a language, then tap Change to {language}.
KaiOS: Press Settings on the apps menu > scroll to the side to select Personalization > scroll down and press Language > press Language > select the language you want to use > press OK or SELECT.
The language selected on your phone will be reflected in WhatsApp Web.
If you're using an Android phone, you might have the option to change WhatsApp's language from within the app. If you don't see this option, it might not be supported in your country.