Hey there,
Thanks for posting. To clarify, it sounds like you’re looking to translate the “First Name” and “Last Name” labels beside your input fields on your site. These translations (field names) are actually controlled by the names of your fields in your actual MailChimp account.
To update these, log in to your MailChimp account, then go to your Lists area to edit your field names. This can be done in your List Settings or your Form Builder (How do I build and design my signup form and response emails?: https://eepurl.com/BQS3r)
Once you’ve updated them in your MailChimp account, then log in to your WP-admin area and go to the MailChimp plugin’s settings. From there, click the update list button to sync your changes and you should see your updated field labels/names take effect.
If you have any other questions, let us know!