Brantree Drop-In has only
https://github.com/braintree/braintree-web-drop-in/tree/master/src/translations
you can translate it manually
Read this document
https://developers.braintreepayments.com/guides/drop-in/setup-and-integration/javascript/v3
Read this document
https://github.com/braintree/braintree-web-drop-in/blob/master/src/translations/en_US.js