User Language

Hello, i’m trying to integrate the Mailchimp order emails in my Woocommerce store, but my users (imported during sync) have no language attached; since my website is only in one language (not english) ho can i force to use always that language in the order confirmation templates?
in my logs i have to following lines:
2022-01-11T14:56:53+00:00 NOTICE order.member.updated :: Updated XXX subscriber status to subscribed and language to
with no language set, how can pass the language to new users and also bulk edit my current subscribers? or even set my language as default

thank you