BTW, at reading the code comments and the tips, the way this plugin is supposed to work is not real...
Basically, even on a monolanguage site where there can be multiple languages installed to let users and Super Users define their preferred UI language, it is the language used by a Super User-1 already logged that will be used to send mail to all Super Users. So basically if Super User-1 prefers an exotic language, others may not even understand the mail...
Simple fix - good spot