as well I have indicated, the easiest way is to use the apk manager but you can also use the apktool.jar
with apktool.jar would be:
1. Loading the framework-res.apk
java -jar apktool.jar if framework-res.apk
2nd. To decompile one .apk
java -jar apktool.jar d <application name> .apk <application name>
java -jar apktool.jar d Launcher2.apk Launcher2
3rd. To compile a apk
java -jar apktool.jar b <application name> <application name> -new.apk
java -jar apktool.jar b Launcher2 Launcher2-new.apk
With this we can change the XML files that are compiled into binary files and modify all .9.png
If we want to translate something, for example an application of the market, the languages are in the resources.arsc
There are applications that sign them if needed, sometimes not.
The best tool to scratch an application is "Eclipse"