If the website ODFAuthors should be improved for the future use the first step would be the change of the localization framework from the old LinguaPlone to the current
plone.app.multilingual and migrate and reindex all content objects. It’s not possible to update the site to the latest Plone without that step.
I already created a Plone buildout for an upgraded ODFAuthors website that is based on version 5.1.x. This buildout is available from the Github repository of The Document Foundation: https://github.com/tdf/odfauthors.org