Problem with RevisionDelete messages

No. The content language text is not being inserted into the log rows. It's just that is forced to the content language for apparently no reason. I'm looking into it.

Is there a i18n-aware way of doing implode( ', ', $changes[1] ) ?

$wgLang->commafy( array );

$wgLang->commafy( ); doesn't work for arrays. It's just for numbers.

The answer seems to be $wgLang->commaList()

Details, details :) It got you checking out Language.php, didn't it? :)