Make en-AU the default language

-- HikaShop version -- : 6.5.2 [2608261812]
-- Joomla version -- : 6.1.3
-- PHP version -- : 8.4.24

I have the following language situation

Joomla en-AU = enabled
Joomla en-AU = default
Joomla en-GB = disabled

HikaShop en-AU = available
HikaShop en-GB = available

How do I force HikaShop to adopt en-AU as the default language and potentially disable en-GB?

I've been chasing language file updates and its doing my head in as both languages are available with HikaShop and some parts of the HikaShop Component are en-GB and others en-AU and emails sent are using one or the other in no particular order.

OK I can edit both Overrides, as a workaround .... but it would be just great to customise one language file and not two

Hoping I'm missing something simple