Area: Optimizely CMS
Applies to versions: 12 and higher
Other versions:
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Note: This documentation is for the preview version of the upcoming release of CMS 12/Commerce 14/Search & Navigation 14. Features included here might not be complete, and might be changed before becoming available in the public release. This documentation is provided for evaluation purposes only.

This topic provides an introduction to the globalization and language management concept for the Optimizely platform, including CMS and Commerce. Globalization is the ability to create and display website content in different languages, and the ability to make the user interface appear in different languages through the localization of user-facing texts.

How does Optimizely know which language to display to visitors?

Optimizely enforces language visibility in the URL, either in the path or the domain part of the URL, because:

  • Search engines, such as Google, must be able to crawl a website and separate content.
  • Users expect to cut and paste a link into an email and send it to someone who can click the link getting the same content.

There also are some technical reasons, such as output caching in .NET, and web browser caching on the client; these expect a single URL to render the same content to anonymous users.

Language concepts

There are three different language concepts in Optimizely, two that are defined by .NET (culture and uiCulture), and one that is the Optimizely CMS content language. See the .NET culture as System Language and uiCulture as User Interface Language. All languages and language settings are expressed as Cultures (as defined by the .NET CultureInfo object). A typical culture is EN-US, which defines the language as English (EN) with the culturally defined specifics for the United States (US). In some cases, you may define the language only, such as SV, which defines the neutral culture Swedish.


  • Culture. An instance of the CultureInfo class; the preferred way of passing language information in Optimizely CMS.
  • Locale. Never explicitly used in Optimizely CMS, except where locale is required by other components. In this case, the locale is read from the LCID property of the required culture, usually CultureInfo.CurrentCulture which corresponds to the system language.
  • Language code. A string that defines the culture to use. See CultureInfo.Name for definition and possible values. If you cannot pass a CultureInfo object, this is the alternative way of specifying language/culture.
  • Candidate match. Many language selection algorithms make use of candidate matches. This means that if you have a language code en-GB, then language code en would be a candidate match. Another possible candidate match for en-GB is en-US. This means that a candidate match is the first language code that matches the substring before the hyphen.

Language setting types

  • System language. Used to control date/time formating, sort order, and so on.
  • User interface language. Controls the localized (translated) resources to display. Determines the language of the user interface, and any other place where calls are made to retrieve and display localized texts.
  • Content language. The preferred language when displaying content. The actual content language is eventually determined by a LanguageSelector and depends on the languages available for the content displayed, because fallback or replacement languages may be applied on the website.

System language

The system language determines how listings are sorted, how to format date and time, and so on. Because these types of formatting rules are culturally dependent, the system language must not be a neutral culture.

The system language is determined by the following rules:

  1. If not in edit/admin user interface, use the content language.
  2. If a user is logged in and a preferred language is set by user, use the personalized language selection for this user.
  3. Use the setting from GlobalizationOptions.CultureLanguageCode. If culture is set to Auto, the language preferences from the web browser are used.

User interface language

The user interface language is used only to pull out localized texts in the web application. It defines the majority of the texts in the Optimizely CMS user interface, but for a site visitor the user interface language applies only to minor elements, such as text on buttons. For a visitor, the majority of information is usually content, which is defined by the content language.

The user interface language is determined by the following rules:

  1. If not in edit/admin user interface, use the content language.
  2. If a user is logged in and a preferred language is set by user, use the personalized language selection for this user.
  3. Use the setting from GlobalizationOptions.UICultureLanguageCode. If culture is set to Auto, the language preferences from the web browser are used.

The preferred way to retrieve localized string resources in Optimizely CMS is through the LocalizationService API. For information about using this, see the Localization service section.

Content language

The content language controls which language version of the content that is displayed. It can be a neutral culture or a specific culture.

The preferred content language is determined by the following rules:

  1. If you have defined the host name to be associated with a specific language, that language is used. The setting is specified under Manage Sites in admin view.
  2. If there is a language segment in the URL (like http://company.com/en/info), that language is used (en).
  3. If you are in the edit view and have selected a specific language site from the Sites section, that language is used.
  4. If the requests contain a query parameter or cookie named epslanguage, use the language defined by the query/cookie.
  5. If the setting GlobalizationSettingsOptions.UseBrowserLanguagePreferences is true, then the language preference from the web browser is used.
  6. Use the language mapped to wildcard host '*' if specified.
  7. Fetch the setting from the GlobalizationOptions.UICultureLanguageCode.
  8. If nothing else is discovered, use the first enabled language branch as defined in Admin / Language Branches, which means that it can be viewed as the default language.

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Last updated: Jul 02, 2021

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