If this is a major PC brand it always includes a full factory warranty and Tech SUpport for a year minimum. If he needs to call, chat or email them to help reset the language he should do so.
If it initially offered English as a language in that regional version then, yes, a reinstall should offer it again. Was he provided with Reinstallation or Recovery media? If not I would have him make the media as a backup and then run Factory Recovery from its partition, or Reinstallation media.