htaccess RewriteRule用于按语言进行子域重定向

I have a website in English http://example.com

Then I want to add code for a redirect to my subdomain PT language http://pt.example.com if the browser language is PT

RewriteEngine on
RewriteCond %{HTTP:Accept-Language} (pt) [NC]
RewriteRule .* http://pt.example.com [R,L]

When I add this I get a redirect loop in the browser.

I have tried example.com/pt and get the same error from the browser.

Add a RewriteCond :

RewriteCond %{HTTP_HOST} !^pt\.example\.com