SignRequest is currently available in 16 languages. You can select your preferred language in the lower right corner.
Note that the language selected is the language used for your own environment while sending the document and for the SignRequest emails that will be sent.
However, once your signer clicks on the 'Review document' button in the email SignRequest automatically detects and selects the language settings of the signer's browser. If SignRequest does not have the language of the signer yet the system will default to English.