Also, there's no compositions, so you have to create the Author property on all document types (File, Image, Article, etc). But this is how we do it, adding metadata to media. It's highly useful. Actually, you may want to make your own custom media doctype for this, and stick to that, regardless of file type. But it wouldn't automatically be default when drag-and-dropping media to the media library.
For the un-multi-lingual-ness, if you restrict the properties on the media doctypes to links/pointers to content-tree items, you can still get the benefits of multi-lingualness, sort of. E.g., the author property isn't a textstring, but a content picker to an author item in the content tree that varies by culture.