The best way to organize the lang strings in a lang file is to alphabetize all of them. Many lang files have attempts to sort the strings by category, but this never works in the long run because it quickly becomes unclear which category new strings should go in.
So I've found that the most convenient way to sort them in the long run is just to alphabetize them. If anyone has some free time, it'd be good to go through all the lang files and alphabetize them. At least, the ones in the core Mahara download. We'd probably need a different process to handle the ones in the translation langpacks.
And of course it wouldn't make sense to do this by hand. You'd want to write a script that identifies the lang files and alphabetizes only the $string['name'] lines. It should be robust enough that it can handle multi-line strings. Comments interspersed amongst the strings should probably be discarded, because these usually refer to the string categories.
Tagging bite-sized, in the sense that it's a relatively large change, but it doesn't require much understanding of how Mahara actually works.