Once XBench has been closed, you can now proceed with the installation of the language.
You can download language packages on the Apsic official website: http://www.apsic.com/blog/?p=20
Once you have downloaded the language package, you have to extract it from the .zip file and manually copy the contents by selecting them and pressing CTRL + C (alternately, with the right click of your mouse, press on Copy)
It is not necessary to copy the file XbenchSpellerOLH.chm because it is already present in the XBench file location in which you are going to paste the contents.