'#translation' added as magic word in Translate extension

One cannot rely on the presence of {{translation}} on the wiki, hence
a parser function has been created to have the same behavior as that of
the template. The function checks for the language code in the page title,
and returns it if it is a valid code. Else, it returns an empty string,
meaning that it is not a translation page.

Bug: 68385
Change-Id: I16bb4fe5294c238aa345e9b33350d64d518748f4
Merge "'#translation' added as magic word in Translate extension"