Adding Additional Customer Tag Based on Language

Dear Shopify Gurus,

I am building my website and using Prestige theme. When a new customer wants to subscribe to my newsletter, I use the double opt-in procedure by Shopify. Automatically, the users that are subscribed to the newsletter are added a tag “newsletter”.

In addition to this tag, I would like another tag that would represent the language that the user selected in the website (english or german). Can you help me with that? I will use this tag in another third party app.

Can you help me with that?

Kind regards,

Ayse