From Stefano's post at http://moodle.org/mod/forum/post.php?reply=463797:

"... because we activated the "My Moodle" option, now the students dont't see anymore the Moodle Home Page.
This is ok, but we need a way to show them the language drop-down list...
This dorp-down, as I can see, is only displayed on home page. ..."

It makes sense to have language selector at My Moodle page, at least in case of my.php being forced instead of standard index.php