'Get the locale string connecting with a language specified by
:attr:`l_lang`.
.. note:: This is a `classmethod`.
:param l_lang: Localized name of a specified language.
:type l_lang: unicode
:return: Locale tag of a specified language.
:rtype: str'

@classmethod
def get_locale_by_language(cls, l_lang):

    for (locl, lang) in cls.language.items():
        if (l_lang == lang):
            return locl
    return 'en_US'
