'Load single n-gram language file given the ISO 639-3 language code
and return its FreqDist'

def _load_lang_ngrams(self, lang):

    if (lang not in self.langs()):
        raise RuntimeError(u'Unsupported    language.')
    crubadan_code = self.iso_to_crubadan(lang)
    ngram_file = path.join(self.root, (crubadan_code + u'-3grams.txt'))
    if (not path.isfile(ngram_file)):
        raise RuntimeError(u'No    N-gram    file    found    for    requested    language.')
    counts = FreqDist()
    if PY3:
        f = open(ngram_file, u'r', encoding=u'utf-8')
    else:
        f = open(ngram_file, u'rU')
    for line in f:
        if PY3:
            data = line.split(u'    ')
        else:
            data = line.decode(u'utf8').split(u'    ')
        ngram = data[1].strip(u'\n')
        freq = int(data[0])
        counts[ngram] = freq
    return counts
