USE enwiki_p;

SELECT /* SLOW_OK */ cl_to

FROM categorylinks left JOIN page on  cl_to=page_title

WHERE cl_from IN (

        SELECT DISTINCT ll_from

        FROM langlinks

        WHERE ll_lang = "fa"

        )

    AND cl_to NOT IN (

        SELECT DISTINCT page_title

        FROM langlinks

        LEFT JOIN page ON page_id = ll_from

        WHERE ll_lang = "fa"

            AND page_namespace = 14

        )

and page_len is not null

GROUP BY cl_to;