Renewing TN , In application for TD , regarding I -539 signature

[bhalderia]

 While renew TN and TD visa by mail.

My wife sign in I-539 in my native language which is same signature as her passport . She also check on box I can read and understand English.

Do she need to sign compulsory in English only in I-539 ? or native language signature will work.

Please share your experience with me. Thanks a lot.