I mean language translations of some components which are distributed separately, not the core Joomla translations. They are marked as unpublished, but this has no effect - components continue to be translated, as language files remain in the respective folders. Looks like Joomla do not care of their status. Is it possible to add some scripts in manifest file to support publishing/unpublishing here?
You can uninstall them. Joomla! finds language files by folder and file name, so publish status is never checked. This is because a file check is usually much faster than a database lookup.
Manifest scripts also only cover install and uninstall AFAIK. You could of course make a system plugin that checked the publish status and disabled or enabled the files accordingly. But there is really no point. The files are simply text, so you can uninstall and reinstall them easily enough.