You can use Localize( "YourSection", "YourVariable", "YourFile" ) this returns your localized string. You will have to place "YourFile.int" into
C:\Program Files\Unreal Tournament 3\UTGame\Localization\[language dir]\
YourFile.int would look like
I am not sure if these language files get downloaded if you place it on a server, i doubt it tbh.
You can always put string into your mutator config file if you define the variable as
var config string Varname
One of the issues I was having with localization was in the UI Editor. I assumed that the Data Browser stored all it's strings in INT files, however it was not working. I just tried placing my UI INT file in the game folder instead of the My Games area. This fixed the problem, although it would be nice if I could use the My Games area. Most likely a bug.