As I touched on in https://bugs.launchpad.net/mahara/+bug/1180544 , there's currently no way for a user looking at the langpacks site ( http://langpacks.mahara.org/ ) to tell whether there's been an update to their language pack.
Therefore, it would be useful if we added version numbers to the language packs. These could be placed in lang/langconfig.php, something like this:
$string['release'] = '1.7.1'; // The Mahara release number this langpack was created for
$string['version'] = '2013052700'; // Incremented on each new release of the langpack, using the current date.
And the name of the langpack file could be changed to something along the lines of "vi-1.7_STABLE-2013052700.tar.gz".
A related idea would be to have specific langpack releases tied to Mahara minor version releases, to support the case where a language string's name is changed in a minor version. In that case, you wouldn't want to upgrade your langpacks before your Mahara version has been upgraded. In that case you'd want langpack releases for each minor version, as well as maybe a "nightly" langpack release.
vi-1.7.3.tar.tgz
vi-1.7.4.tar.tgz
vi-1.7_STABLE-2013052700.tar.gz
On a related note, it would probably be handy if there was an admin page that listed the currently installed languages and what their release and version numbers are. This may require adding another language string to langconfig.php with the name of the language.