Since the introduction of default.php and defaultconfig.php in XH 1.5 that's probably not necessary. If a string is missing, it will be automatically taken from the default file. This is explained in detail in the
XH-Wiki (the handling of defaultconfig.php is analogeous).
But the "defaults" don't cater for removed strings (well, actually they don't hurt much, but in the long run they should be stripped off; I believe that Translator_XH does this, but I'm not sure), but what's worse, the technique doesn't work for important changes. E.g.: when a plugin author changes the meaning of a setting and the according help text, this might go unnoticed.
Anyway, it would be nice to have the possibility to do an easy update, as it's possible with other software too (e.g. Firefox' and Thunderbird's Update is absolutely painless, won't change any customizations and even checks for the compatibility of plugins). But this will take some time to do for CMSimple_XH, so we should concentrate on the update availability check first, as this is a prerequisite for the automatic update.