Analysis using BuiltWith shows that the site is coded with PHP, Perl and Java. Smells like real enterprise decisions right there. I’m no expert but I’d be guessing that the Perl is likley the remains coming from the old code base. That’d be fair yeah? Haven’t heard of many people coding websites with Perl in 2025.

https://builtwith.com/bom.gov.au

It has data-drupal attributes in the source. Not sure where the Perl and Java things would have come from.