How do strings work in JASS?

If I want to display a text message, right the way I'm doing it is.

set udg_(my string variable) = Externalize String ( "Blah Blah" )

Then I display the message using nativeDisplayText functions.

My question is how do I view the amount of strings of my map. TRIGSTR_1392 for example has something. If I change it in GUI then convert to JASS again, it's TRIGSTR_1421 for some reason. I want to know what happened to the other tons of strings? That way I can remove them if their in the map file still.

open war3map.wts (warcraft 3 trigger strings) of the map with an mpq editor (or use File->Export Strings)
(use notepad)

Externalize String

not for "normal" maps, dont use this function.