It seems, if you download a language file directly from Transifex (using the "download" option and not the "download to translate" option, the language strings that weren't translated yet get filled up by the original English language strings. I've just checked it using the Italian language files. Maybe a similar thing happens when the translations get pulled from Transifex to github. The question is: how is the "completeness" handled? The ca.php is only 94% complete, so should it even get included currently or is the required completeness less than 100%?