MySQL 8.0

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WITH param AS (
  SELECT
      2 AS primary_domain_id,    -- id первичного домена
      1 AS secondary_domain_id,  -- id вторичного домена
      2 AS primary_language_id,  -- id первичного языка
      1 AS secondary_language_id -- id вторичного языка
    FROM dual
)
SELECT *
  FROM (
    SELECT m.*,
        row_number() over (
          partition by m.movie_id
          order by
          	case
          	  when m.domain_id = p.primary_domain_id then 100
          	  when m.domain_id = p.secondary_domain_id then 50
          	  else 1
            end DESC,
          	case
          	  when m.language_id = p.primary_language_id then 100
          	  when m.language_id = p.secondary_language_id then 50
          	  else 1
            end DESC
        ) rn
      FROM `movie_desc` m, param p
      WHERE (m.domain_id = p.primary_domain_id
          OR m.domain_id = p.secondary_domain_id
          OR m.domain_id IS NULL)
	    AND (m.language_id = p.primary_language_id
          OR m.language_id = p.secondary_language_id
          OR m.language_id IS NULL)
  ) t
  WHERE t.rn = 1
;

id	description	movie_id	domain_id	language_id	rn
3	Русское описание фильма #1 для сайта #2	1	2	2	1
8	Русское описание фильма #2 для сайта #2	2	2	2	1