SELECT 
  b.*, 
  d.*, 
  c.* 
FROM 
  cscart_bm_blocks as b 
  LEFT JOIN cscart_bm_blocks_descriptions as d ON b.block_id = d.block_id 
  LEFT JOIN cscart_bm_blocks_content as c ON b.block_id = c.block_id 
  AND d.lang_code = c.lang_code 
WHERE 
  b.block_id = 251 
  AND d.lang_code = 'fr' 
  AND (
    (
      c.object_id = 661 
      AND c.object_type like 'products'
    ) 
    OR (
      c.object_id = 0 
      AND c.object_type like ''
    )
  ) 
ORDER BY 
  snapping_id DESC 
LIMIT 
  1

Query time 0.00028

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "b",
      "access_type": "const",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "4",
      "used_key_parts": ["block_id"],
      "ref": ["const"],
      "rows": 1,
      "filtered": 100
    },
    "table": {
      "table_name": "d",
      "access_type": "const",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "10",
      "used_key_parts": ["block_id", "lang_code"],
      "ref": ["const", "const"],
      "rows": 1,
      "filtered": 100
    },
    "table": {
      "table_name": "c",
      "access_type": "ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "4",
      "used_key_parts": ["block_id"],
      "ref": ["const"],
      "rows": 8,
      "filtered": 100,
      "attached_condition": "c.block_id <=> 251 and c.lang_code = 'fr' and (c.object_id = 661 and c.object_type like 'products' or c.object_id = 0 and c.object_type like '')"
    }
  }
}