You want to make the Pending and Welcome emails within CB > Configuration > Registration multilingual? If I understood correctly you need to use language defines to do this. Example as follows.
Subject: _UE_PENDING_EMAIL_SUBJ
Body: _UE_PENDING_EMAIL_BODY
Then within your CB language file (see your CB documentation for locations). You'd define your new string. Example as follows.
define( '_UE_PENDING_EMAIL_SUBJ', 'Registration Pending' );
define( '_UE_PENDING_EMAIL_BODY', 'Hello, thanks for registering!' );
See your CB documentation available for download in the Advanced downloads section for further usage information. You can also review the below tutorial regarding localization in CB.
www.joomlapolis.com/support/tutorials/106-localization/18210-customizing-your-cb-language