It works perfectly for me, follow this steps:

Move the folder to the place you have the GeekTool scripts

If you want the text in german (de), spanish (es), french (fr), italian (it), japanese (jp), dutch (nl):
open the "weather_localization_jp.rb" you want (I use the sp one)

    on top you can see:
            ### CONFIG [ THESE VALUES OVERRIDE weatherparser.rb ]
            # "City, State" or "City, Country" or ZIP Code
            $mycity = 'Madrid, Spain'
            # f for fahrenheit, c for celsius
            $f_or_c = 'c'
            # folder where the weather icons are located, no trailing slash
            $basedir = '~/Dropbox/WeatherIcons'

    change to the city and country you want
            $mycity = 'Buenos Aires, Argentina'

    choose the unit (c is ok for me)

    get the path to the "GeekToolWeatherLocalized1.2" folder
    (the best way to get it is opening terminal and drag the folder on it, you will get the full path)
            $basedir = '/Users/genimac/Documents/GeekToolWeatherLocalized1.2'
            or
            $basedir = '~/Documents/GeekToolWeatherLocalized1.2'

    open the "weatherparser.rb"

    on top you see:
            # If you're using localization, skip the config in this file
            # and set your values in weather_localization.rb

            localization_file = "weather_localization_fr.rb"
            # For non-english languages, change the filename to match your localization file
            # e.g. localization_file = "weather_localization_es.rb"
            # The default file is blank and will use English automatically,
            # and setting localization_file to false will remove the requirement for the
            # additional file completely.

    Change to the language you want
            localization_file = weather_localization_sp.rb   (the spanish I want)

    Done, now go to the geeklet part.

Iy you want the text in english:
you only need to edit the "weatherparser.rb"
Change to english
localization_file = weather_localization.rb

    Now edit the city, units and path as before
            # CONFIG [ THESE VALUES WILL BE OVERRIDDEN BY YOUR LOCALIZATION FILE ]
            # "City, State" or "City, Country" or ZIP Code
            $mycity = '55987'
            # f for fahrenheit, c for celsius
            $f_or_c = 'f'
            # folder where the weather icons are located, no trailing slash
            $basedir = '~/Dropbox/WeatherIcons'
            ### END CONFIG

Finally you need to adjust the paths on the geeklet itself
open GeekTool preferences
select the time geeklet
change the command from "~/Dropbox/WeatherIcons/weatherparser.rb time" to your path
"~/Documents/GeekToolWeatherLocalized1.2/weatherparser.rb time"

    Do the same for "conditions" and "forecast"
    for the weather icon change the URL field from "file://localhost/Users/ttscoff/Dropbox/Code/projects/weathericons2/weathericon.png"
    to "~/Documents/GeekToolWeatherLocalized1.2/weathericon.png"

    Now look for a nice color, font and sizes to match your desktop.