Networking & Infrastructure

Smartling Headers

This article is for Account Owners and Project Managers using the Global Delivery Network.

When a user requests pages on your localized site, the Global Delivery Network (GDN) will add additional headers when retrieving content from your source site. These headers are useful for identifying traffic on your localized site and serving custom content.

To learn how to use headers, see Display Language-Specific Content.

View Headers

To view all headers that are sent from the Global Delivery Network to your source site, you can append /__smartling/api/headers.htm to the end of any URL on your localized site (i.e The resulting page will show you all headers that are sent to the source domain.

For information on additional preview modes, see Global Delivery Network Preview Modes.


The X-Language-Locale is a custom request header added by the GDN. This header specifies the language being requested. You can use a web server configuration (i.e Apache, Nginx) or server side logic (i.e PHP, Node.js) to detect this header and its value. 

Format of the header: 

X-Language-Locale: [language_code]-[COUNTRY_CODE]

For example:

  • French (France): X-Language-Locale: fr-FR
  • French (Canada): X-Language-Locale: fr-CA
  • English (United Kingdom): X-Language-Locale: en-GB
  • Spanish (International): X-Language-Locale: es
  • Russian: X-Language-Locale: ru-RU

To find out the value of your custom header:

  1. Do one of the following: 
    • In the New Experience, from your GDN project, click the gear icon > Project Settings > Domains, then click the globe icon. 
    • In the Classic Experience, from within the Smartling Dashboard, select Global Delivery Network > Domains then click the globe icon.
  2. Click the localized domain. Then click on the Arrow next to the language and choose Edit Localized Domain. The value next to X-Language-Locale displays the value that the GDN will send for the X-Language-Locale header. To change this value to use underscore instead of dash, click on the drop down down to make your change, then click Save.

Other Headers


The X-Forwarded-For request header will identify the originating IP address of the request. Since your source site will only see the Global Deliver Network IP addresses, this header is useful for identifying the IP address of your end user.

For more information visit


The X-Forwarded-Proto request header will identify the HTTP protocol (http or https) of the end user making the request. Smartling will not automatically redirect to https and will retain the protocol used by the end user. This header will have a value of http or https. 

For more information visit


The X-Forwarded-Port request is the port that the end user used to access your site. This will usually be 80 for HTTP and and 443 for HTTPs.


The X-Amzn-Trace-Id request header is added by our load balancer for troubleshooting purposes.

If you would like to send any other custom headers on your localized site, please contact your Smartling Customer Success Manager or use an Advanced GDN Rule.

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