Import and load a Language class.

    lang (unicode): Two-letter language code, e.g. 'en'.
    RETURNS (Language): Language class.

def get_lang_class(lang):
    """Import and load a Language class.

    lang (unicode): Two-letter language code, e.g. 'en'.
    RETURNS (Language): Language class.
    """
    global LANGUAGES
    # Check if an entry point is exposed for the language code
    entry_point = get_entry_point("spacy_languages", lang)
    if entry_point is not None:
        LANGUAGES[lang] = entry_point
        return entry_point
    if lang not in LANGUAGES:
        try:
            module = importlib.import_module(".lang.%s" % lang, "spacy")
        except ImportError as err:
            raise ImportError(Errors.E048.format(lang=lang, err=err))
        LANGUAGES[lang] = getattr(module, module.__all__[0])
    return LANGUAGES[lang]