Go as Admin into Administration, add the Flash app extension and follow the progress logs.
At a point, you will see this warning at the Flash Translation install step: "The [org.xwiki.localization.wiki.internal.ComponentDocumentTranslationBundle] listener is overwritting a previously registered listener [org.xwiki.localization.wiki.internal.ComponentDocumentTranslationBundle] since they both are registered under the same id [localization.bundle.document:xwiki:Flash.Translations]. In the future consider removing a Listener first if you really want to register it again."
Even with this warning, the installation is finished.
Bug
Minor
