as discussed with Alex Chow and Juan Fernandez, there are some places, where one can't provide a translation for fields in the document and media library, although it would make sense to have this possibility
When creating a folder in the DML you can provide a description but you can't translate the description
2) Document Types
When creating a document type you can provide translations for all the custom fields you can visually add to the document type, unfortunately there is no option to add a translation for the description of the document type.
3) When adding a file to the document library, there is also no option to provide a translation for the description. As discussed during lunch with Alex Chow, it doesn't make sense to translate the title since the title will become the filename in the DML and it would be hard to manage a translated filename (what happens if the file gets renamed from WEBDAV etc) but the description should be translatable
I will add to this list if I find other places...