As other have pointed out, there is no built-in function as this likely due to the reality of many countries having multiple languages. So unfortunately, I can't point you to a library that does this, but I did go ahead and write a little function which does what you want.
There are two caveats, one being if it isn't provided a language it will just pick the first locale in the list. To get around this, you'd have to put some logic around the function call to provide it with the appropriate language. The other is that it needs to have php5-intl installed.
<?php
/**
/* Returns a locale from a country code that is provided.
/*
/* @param $country_code ISO 3166-2-alpha 2 country code
/* @param $language_code ISO 639-1-alpha 2 language code
/* @returns a locale, formatted like en_US, or null if not found
/**/
function country_code_to_locale($country_code, $language_code = '')
{
// Locale list taken from:
// http://stackoverflow.com/questions/3191664/
// list-of-all-locales-and-their-short-codes
$locales = array('af-ZA',
'am-ET',
'ar-AE',
'ar-BH',
'ar-DZ',
'ar-EG',
'ar-IQ',
'ar-JO',
'ar-KW',
'ar-LB',
'ar-LY',
'ar-MA',
'arn-CL',
'ar-OM',
'ar-QA',
'ar-SA',
'ar-SY',
'ar-TN',
'ar-YE',
'as-IN',
'az-Cyrl-AZ',
'az-Latn-AZ',
'ba-RU',
'be-BY',
'bg-BG',
'bn-BD',
'bn-IN',
'bo-CN',
'br-FR',
'bs-Cyrl-BA',
'bs-Latn-BA',
'ca-ES',
'co-FR',
'cs-CZ',
'cy-GB',
'da-DK',
'de-AT',
'de-CH',
'de-DE',
'de-LI',
'de-LU',
'dsb-DE',
'dv-MV',
'el-GR',
'en-029',
'en-AU',
'en-BZ',
'en-CA',
'en-GB',
'en-IE',
'en-IN',
'en-JM',
'en-MY',
'en-NZ',
'en-PH',
'en-SG',
'en-TT',
'en-US',
'en-ZA',
'en-ZW',
'es-AR',
'es-BO',
'es-CL',
'es-CO',
'es-CR',
'es-DO',
'es-EC',
'es-ES',
'es-GT',
'es-HN',
'es-MX',
'es-NI',
'es-PA',
'es-PE',
'es-PR',
'es-PY',
'es-SV',
'es-US',
'es-UY',
'es-VE',
'et-EE',
'eu-ES',
'fa-IR',
'fi-FI',
'fil-PH',
'fo-FO',
'fr-BE',
'fr-CA',
'fr-CH',
'fr-FR',
'fr-LU',
'fr-MC',
'fy-NL',
'ga-IE',
'gd-GB',
'gl-ES',
'gsw-FR',
'gu-IN',
'ha-Latn-NG',
'he-IL',
'hi-IN',
'hr-BA',
'hr-HR',
'hsb-DE',
'hu-HU',
'hy-AM',
'id-ID',
'ig-NG',
'ii-CN',
'is-IS',
'it-CH',
'it-IT',
'iu-Cans-CA',
'iu-Latn-CA',
'ja-JP',
'ka-GE',
'kk-KZ',
'kl-GL',
'km-KH',
'kn-IN',
'kok-IN',
'ko-KR',
'ky-KG',
'lb-LU',
'lo-LA',
'lt-LT',
'lv-LV',
'mi-NZ',
'mk-MK',
'ml-IN',
'mn-MN',
'mn-Mong-CN',
'moh-CA',
'mr-IN',
'ms-BN',
'ms-MY',
'mt-MT',
'nb-NO',
'ne-NP',
'nl-BE',
'nl-NL',
'nn-NO',
'nso-ZA',
'oc-FR',
'or-IN',
'pa-IN',
'pl-PL',
'prs-AF',
'ps-AF',
'pt-BR',
'pt-PT',
'qut-GT',
'quz-BO',
'quz-EC',
'quz-PE',
'rm-CH',
'ro-RO',
'ru-RU',
'rw-RW',
'sah-RU',
'sa-IN',
'se-FI',
'se-NO',
'se-SE',
'si-LK',
'sk-SK',
'sl-SI',
'sma-NO',
'sma-SE',
'smj-NO',
'smj-SE',
'smn-FI',
'sms-FI',
'sq-AL',
'sr-Cyrl-BA',
'sr-Cyrl-CS',
'sr-Cyrl-ME',
'sr-Cyrl-RS',
'sr-Latn-BA',
'sr-Latn-CS',
'sr-Latn-ME',
'sr-Latn-RS',
'sv-FI',
'sv-SE',
'sw-KE',
'syr-SY',
'ta-IN',
'te-IN',
'tg-Cyrl-TJ',
'th-TH',
'tk-TM',
'tn-ZA',
'tr-TR',
'tt-RU',
'tzm-Latn-DZ',
'ug-CN',
'uk-UA',
'ur-PK',
'uz-Cyrl-UZ',
'uz-Latn-UZ',
'vi-VN',
'wo-SN',
'xh-ZA',
'yo-NG',
'zh-CN',
'zh-HK',
'zh-MO',
'zh-SG',
'zh-TW',
'zu-ZA',);
foreach ($locales as $locale)
{
$locale_region = locale_get_region($locale);
$locale_language = locale_get_primary_language($locale);
$locale_array = array('language' => $locale_language,
'region' => $locale_region);
if (strtoupper($country_code) == $locale_region &&
$language_code == '')
{
return locale_compose($locale_array);
}
elseif (strtoupper($country_code) == $locale_region &&
strtolower($language_code) == $locale_language)
{
return locale_compose($locale_array);
}
}
return null;
}
?>
