Generally, all your languages have to be assigned to a domain and/or market in Shopify. Should an additional language not be assigned in Shopify correctly, you will see this error in your langify languages section:

It is easy to fix. Simply click on “Here” as indicated above to get your “Domains & languages” section in Shopify and assign your language(s) accordingly. 

Here a quick Video:

Hint: You can also go there in Shopify directly:
Settings > Markets > Domains and Language > assign language to domain/market