Middleware for language/region locale handling.

Some websites need to show different translated or geographical market-specific content. This middleware makes use of a variety of explicit and implicit factors to provide the most appropriate content.

Query Parameters

A ?locale= query parameter may be included in a page request that indicate an explicit adjustment. The ?locale= query parameter can be the resulting page URLs fetched in service to a locale menu.

Alternatively, the ?region= or ?language= query parameters may provide vauge hints.

Cookies

For the convenience of the end-user, explicit language selection should be remembered across sessions. The locale cookie values are not PII.

Initial URL Path Element

In order to "cache bust" and have an immediate effect upon changing a locale, post-locale-selection page paths start with the new locale.

Browser Language

Browsers and operating systems may provide language preference(s) via the Accept-Language header. The language (and subtag) can imply a locale.

GeoIP

The client IP address suggests a country, which further implies a locale.

Some Combination

Combining vague query parameters (e.g., ?language= or ?region=), browser languages (especially en or es), and GeoIP countries (e.g. Canada) can have a combined effect in picking the most appropriate language.