What forms of root URLs are acceptable to indicate website language version?

Only one language version format is supported, which is the equivalent of the website root folder and consists of one or optionally two values, separated by a dash. The first two-character language code is in ISO 639-1 format, which may be followed by an optional second code representing the region in ISO 3166-1 Alpha 2 format. Examples of valid URLs for language versions:

• http://mydomain.com/en
• http://mydomain.com/en-US