I have just being {{nsd}} tagging 100 unsourced images from the OsamaK
list at
http://commons.wikimedia.org/wiki/User:OsamaK/Tagging
<spam>Go and help tagging!</spam>
For each image, i tagged <no source> with UserMessages.js trying to
guess the user language, and for users with user page/seeming to be the
authors/many images (they often have a bunch of unsourced images with
the same license) i also notified them in their home wiki (these are old
images, we can't expect they're checking their commons talk if they
haven't contributed for months!).
The 'notifications' were a line from the localised image source template
with a link to their commons talk page. My message may be nonsense, but
i hope they will understand and figure out they should go to commons and
(seeing the full template) source their images ;-)
Doing it i found out that:
*My guesses were quite good (they *had* an account there).
*It's fast to create a new account (i made 4 and used several more).
*A good way to detect the user language/home wiki is to check-usage
where is the tagged image being used.
*Leaving messages on RTL is hard.