How can I get the browser language in node.js (express.js)?

You can use req.headers["accept-language"] to get the language/locale the user has set in his browser.

For easier support, you may want to look into a locale module.

request.acceptsLanguages will contain a parsed version of request.headers['accept-language'].

See: http://expressjs.com/en/api.html#req.acceptsLanguages