I can add a new MIME type in shared MIME-info, but how can I associates this MIME type with an application?
if you just want to associate them directly, and not make them default, you can add them to
xdg-mime, as geekosaur suggests, might perhaps be more robust. In this case, you would want
xdg-mime install [--mode mode] [--novendor] mimetypes-file
Adds the file type descriptions provided in
mimetypes-fileto the desktop environment.
mimetypes-filemust be a XML file that follows the freedesktop.org Shared MIME-info Database specification and that has a mime-info element as its document root. For each new file type one or more icons with name major-minor must be installed with the
xdg-icon-resourcecommand in the mimetypes context. For example the
application/vnd.oasis.opendocument.textfiletype requires an icon by the name of
application-vnd.oasis.opendocument.textto be installed.
xdg-mime defaultapplication mimetype
Ask the desktop environment to make application the default application for opening files of type mimetype. An application can be made the default for several file types by specifying multiple mimetype s.
The above is taken from
man xdg-mime, slightly modified to copy the usage down from the SYNOPSIS.