Avoid automatic IP-based language redirects
Automatically redirecting visitors to a locale based on IP geolocation or Accept-Language is an anti-pattern. It traps users in the wrong language, breaks search crawlers, and breaks shared links. Let users choose.
Google Search Central — Managing multi-regional and multilingual sites
W3C i18n — When should I use language negotiation?
W3C i18n — Using select to link to localized content