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?

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).

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.

> Imperfect implementations > > Starting in 1985, ISO 3166-1 alpha-2 codes have been used in the > Domain Name System as country code top-level domains (ccTLDs). The > Internet Assigned Numbers Authority currently assigns the ccTLDs > mostly following the alpha-2 codes, but with a few exceptions.[9] For > example, the United Kingdom, whose alpha-2 code is GB, uses .uk > instead of .gb as its ccTLD, as UK is currently exceptionally reserved > in ISO 3166-1 on the request of the United Kingdom.

According to wikipedia http://en.wikipedia.org/wiki/ISO_3166-1_alpha-2.

So apparently it's an old thing that has stuck or something like that.

EDIT: martin clayton found a better answer.

You cannot simply invent locales! They are already defined. So "en-gb" is British English, whereas "en-us" is American English. If you use "en-uk", you are just making up a code.

As to why the official code is "en-gb" and not "en-uk", I think basically because there is no such thing as United Kingdom English. The language variant is British. Note that the difference between Great Britain and the United Kingdom is:

UK = GB + Northern Ireland

So by naming the variant "en-UK" it's as if you are saying that you want to include the way they speak in Northern Ireland within this category. But why would you want to do that? From a linguistic perspective it makes no sense, as Northern Ireland English is closer to Irish English (en-IE) than British English.

the correct country code in ISO 3166 for the United Kingdom of Great Britain and Northern Ireland is for some reason "GB", so the locale code should be en_GB, and not en_UK as noted here.

en_GB is also used by glibc, gnome, kde, etc

Also i like the fact that many previous bug fixes in opensource projects are related to this like in apache http 1.3 and roundcube project