Well, it's more complex than that because generally you'd have a single file for email templates within a plugin (keeping them all together), and you'd want to exclude that from the list that the language area generates - which includes all files with the filename.language.php setup in every folder of every active plugin (it's good like that)
But unless you tell the language editor about the file it's still going to include it, even if it turns out there are no usable language strings there if that makes sense.
The splice-into-DB still needs to be done, IMO, for strings that would like to be available very commonly (e.g. that would like to be part of index)