Sorry me english:

how can I install the Italian language in the form phpBB?

I have not seen other users attempt this. Have you tried in the Italian WD Community for suggestions?

WD Forum Italiano

because at least you answered me, are five days that no one answers and I did not know what to do, unfortunately the Italian forum and not 'a great thing

There’s more activity on the English boards because they are older. I’m sorry you have been unable to obtain an answer, but hopefully an experienced User will be able to assist, if possible.