Replace availableLanguages() with allLanguages()

Why? If we want the page's "Use the main language if there is no
prioritized translation." to control whether or not the untranslated page
appears in a siteaccess, we need to remove all the prioritized translations
from site.ini. That works fine, except for creating the new translation.
By replacing availableLanguages() with allLanguages() we can still base
the new translation on the main language even though there are no
available languages in the siteaccess.