How do you say which country are you from in French informally?

Dans quel pays es-tu?

You can also say (formally)

"De quel pays êtes-vous venu/venus/venue/venues?"
depending on the gender and number of persons to whom you're addressing.

To say "Which country are you from?" informally in French, you can use the following phrase:

"De quel pays viens-tu ?"

Now, let me break it down for you:

1. "De" means "from."
2. "Quel" means "which."
3. "Pays" means "country."
4. "Viens-tu" is the informal way of saying "are you from?" It is formed by combining the verb "venir" ("to come") and the pronoun "tu" ("you").

So, when you put it all together, you get "De quel pays viens-tu ?" which means "Which country are you from?" in an informal way.

If you want to use a more formal way of asking the same question, you can use "De quel pays venez-vous ?" where "vous" is the formal version of "you."