def METHOD_NAME(language: str, k1: Optional[float]=None, b: Optional[float]=None) -> (Searcher, str):
    searcher = LuceneSearcher.from_prebuilt_index(f'miracl-v{VERSION}-{language}')
    searcher.set_language(language)
    if k1 is not None and b is not None:
        searcher.set_bm25(k1, b)
        retriever_name = f'BM25 (k1={k1}, b={b})'
    else:
        retriever_name = 'BM25'
    return searcher, retriever_name