Nginx redirect with Lua based on browser language

Question

I have a wordpress multisite with nginx, and I have been trying to find a way to redirect users based on their browser language.

Thanks to Mark and Joris I was able to redirect in most cases, but I have one problem.

Here are my situations and code for your information.

1. My situations
   • My multisite setup is in subdomains. My main site is in Korean and other two sites are in Japanese and English.
   • Obviously I want to redirect Japan users to Japanese site and international users to English site, and I think I figured this out.
   • But, if I want to go to the main Korean site from subdomain sites, I keep getting redirected back to jp.domain.com or en.domain.com. There would not be many use cases like this, but I think this should be possible.

2. Code

   location = / {
       default_type text/html;
   
       rewrite_by_lua '
       if ngx.var.cookie_lang == "ko" then
           return
       elseif ngx.var.cookie_lang == "ja" then
           ngx.redirect("http://jp.domain.com/")
           return
       elseif ngx.var.cookie_lang == "en" then
           ngx.redirect("http://en.domain.com/")
           return
       end
   
       if ngx.var.http_accept_language then
           for lang in (ngx.var.http_accept_language .. ","):gmatch("([^,]*),") do
               if string.sub(lang, 0, 2) == "ko" then
                   ngx.header["Set-Cookie"] = "lang=ko; path=/"
                   return
               elseif string.sub(lang, 0, 2) == "ja" then
                   ngx.header["Set-Cookie"] = "lang=ja; path=/"
                   ngx.redirect("http://jp.domain.com/")
                   return
               end
           end
       end
   
       ngx.header["Set-Cookie"] = "lang=en; path=/"
       ngx.redirect("http://en.domain.com/")
       ';
   }
   
   location / {
       try_files $uri $uri/ /index.php?$args;
       rewrite_by_lua '
       if ngx.var.arg_lang == "ko" then
           ngx.header["Set-Cookie"] = "lang=ko; path=/"
       elseif ngx.var.arg_lang == "ja" then
           ngx.header["Set-Cookie"] = "lang=ja; path=/"
       elseif ngx.var.arg_lang == "en" then
           ngx.header["Set-Cookie"] = "lang=en; path=/"
       end
       ';
   }
   

Any help would be appreciated.