I used monolingual to delete languages and accidentally deleted some of the English sub languages like English (u.s.).
How can I re install the languages?
Yes, a reinstall is your only option. Monolingual gives very specific warnings on what may happen if you do not double check what you have asked it to delete. Unless you are desperately trying to retrieve a small part of free space, I would highly recommend not using such programs, as you have found out. A reinstall (do backup though) should install a full system including languages and leave your other data untouched.