I did try that but it only works for English (not to mention skins then have to supply another 3MB+ set of backdrops as other plugins use the weather codes for file names).In my opinion you can use the condition label for this (#WorldWeather.TodayCondition), in your skin file you use the texture value <texture>#WorldWeather.TodayCondition.png</texture> (e.g. if condition is "sunny" the skin engine is looking for sunny.png").
I think I'm to dump to install. Tried it using the installation instruction (pdf) but I don't have the mentioned directories (skin etc.). Tried to find the mpe1, but no chance...