import re


def _translate_lang(lang):
    """
    Returns `value` from `lang` expected to be like 'LANG=value'.
    """
    match = re.search(r"^LANG=(.*)$", lang)
    if not match:
        raise RuntimeError("Need LANG=xx_XX argument.")
    value = match.group(1)
    if not value:
        raise RuntimeError("Need LANG=xx_XX argument.")
    return value