Considering what you say, you provide a perfect
argument why NOT to localise
the user interface of an extinct language. So far we have always insisted on
a localised UI.
We insist on a localised UI because it makes it easier for the
intended users (ie. speakers of the language) to use the site. Who are
the intended users of a Wikipedia in an extinct language? Wikipedia
exists to spread knowledge, how does a Wikipedia in an extinct
language further that aim?