yaourt -S jdownloader
i have installed it a month ago. it worked without any problems.
yaourt -S jdownloader2
does not work anymore. i do not know exactly why, but it seems the PKGBUILD is totally broken.
in order to install jdownloader2, i did this:
yaourt -S jdownloader2-beta
this will not install successfully. do not mind.
2. go here: http://jdownloader.org/download/offline
and download the right linux installer (.sh file or shell file) for your system. copy the shell file into your ~/.jdownloader2/ directory and execute it.
in kde you can double click it. in other DEs you might execute it in your terminal. maybe, you need to make it executable before you can execute it. if you have questions regarding this, please ask specific questions and give us the terminal output/error message.