Wikimedia Bugzilla is closed!

There is no way currently to determine (the) language(s) of a page title
beyound some heuristics which are mere guesswork,
Yet for proper language tagging in html, language and directionality need
to be known.

Fortunately, theses case are comparatively rare in current wikis, as
far as I know, but you can easily find samples of mixed language/script
page title, such as disambiguations in a dictionary:
  blow (hit)
  blow (airstream)
  etc.
where the words in brackets may get translated to chinese when the
target language is chinese.

It is of course impossible to insert <span> tags with language informations
into page titles.

For the correct rendering of a page title on the respective page, we
can use the PAGETITLE function.

It may be an option, to use that information elsewhere, too, such as in
logs, in lists, and in link anchors, for instance. The latter would
make the parser automatically convert [[pagename]] to something like
[[pagename|PAGETITLE attribute of pagename]] if that PAGETITLE exists.
Evaluation of [[pagename|]] would have to be moved from pre-parse to
rendering, or a new paser function PAGETITLEOF:title|options be used.
All these would need the (current) pagetitle be kept in the database.

(Note that this would be yet another piece of design breaking our so
called "permalinks")