When you create a natively compiled stored procedure you must specify the language; there is no default. This is somewhat irritating, because most of the time you don't care (and you should not care). However, it turns out that you can specify a bogus language. You get two error messages, but the procedure is nevertheless created. The language appears to be us_english in this case, although I have made investigation from where the default is taken.
Not really sure if this is a bug, but I report it anyway.