How to keep language settings from resetting after a page refresh?

[torena]

Hello,

I've recently changed my site from a headless solution to a Shopify theme and I'm unable to get translations working. If you navigate to https://torena.store/ you will receive a popup to change language, which for example changes to dutch. But if you refresh the page back to https://torena.store/ it is reset to english. How do I make sure that a returning dutch speaking customer that goes to https://torena.store/ redirects to https://torena.store/nl automatically since they've already selected their language earlier. 
I don't see a cookie being set either for language.