Is en_UK an illegal locale?

So far I had always used 'en_UK' for British English. Today I got an error when using it with Zend Framework because the locale is not included in the long list of recognized locales.

Here's just a short extract of that list:

'ee_GH' => true, 'ee_TG' => true, 'ee'    => true, 'el_CY' => true, 'el_GR' => true,
'el'    => true, 'en_AS' => true, 'en_AU' => true, 'en_BE' => true, 'en_BW' => true,
'en_BZ' => true, 'en_CA' => true, 'en_GB' => true, 'en_GU' => true, 'en_HK' => true,
'en_IE' => true, 'en_IN' => true, 'en_JM' => true, 'en_MH' => true, 'en_MP' => true,
'en_MT' => true, 'en_NA' => true, 'en_NZ' => true, 'en_PH' => true, 'en_PK' => true,
'en_SG' => true, 'en_TT' => true, 'en_UM' => true, 'en_US' => true, 'en_VI' => true,
'en_ZA' => true, 'en_ZW' => true, 'en'    => true, 'eo'    => true, 'es_AR' => true,
'es_BO' => true, 'es_CL' => true, 'es_CO' => true, 'es_CR' => true, 'es_DO' => true,

As you can see, there are all kinds of territories with English language and there is also an entry 'en_GB' which I assume stands for Great Britain... but there is no 'en_UK'. Is that just a 'bug' in Zend Framework or is there another reason for that?

Solution 1:

The correct country code is en_GB. Locales use ISO 3166-1 for country codes. The wikipedia writeup includes:

The codes are chosen, according to the ISO 3166/MA, "to reflect the significant, unique component of the country name in order to allow a visual association between country name and country code".[7] For this reason, common components of country names like "Republic", "Kingdom", "United", "Federal" or "Democratic" are normally not used for deriving the code elements. As a consequence, for example, the United Kingdom is officially assigned the alpha-2 code GB rather than UK, based on its official name "United Kingdom of Great Britain and Northern Ireland" (although UK is reserved on the request of the United Kingdom).

Solution 2:

It is indeed a common (?) mistake. en_UK is wrong. The ISO country code for the UK is GB, making the language tag en_GB.