SELECT 
  pfv.variant_id, 
  pfv.position, 
  pfvd.variant 
FROM 
  cscart_product_feature_variants AS pfv 
  INNER JOIN cscart_product_feature_variant_descriptions AS pfvd ON pfv.variant_id = pfvd.variant_id 
  AND pfvd.lang_code = 'en' 
WHERE 
  pfv.variant_id IN (
    1973, 2455, 2448, 2477, 1694, 2122, 2473, 
    1659, 1660, 2344, 2345, 2452, 2479, 
    2350, 2480, 2481, 1462, 2443, 2471, 
    2457, 1972, 1902, 1992, 2139, 1718, 
    2482, 2075, 2413, 1926, 1995, 1904, 
    2000, 2447, 2478, 2451, 1787, 1905, 
    1900, 2464, 2466, 2467, 2463, 2468, 
    2489, 2490, 1876, 2123, 2485, 2486, 
    2124
  )

Query time 0.00120

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "52.51"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id"
          ],
          "key_length": "3",
          "rows_examined_per_scan": 50,
          "rows_produced_per_join": 50,
          "filtered": "100.00",
          "index_condition": "(`test2_gaseus`.`pfv`.`variant_id` in (1973,2455,2448,2477,1694,2122,2473,1659,1660,2344,2345,2452,2479,2350,2480,2481,1462,2443,2471,2457,1972,1902,1992,2139,1718,2482,2075,2413,1926,1995,1904,2000,2447,2478,2451,1787,1905,1900,2464,2466,2467,2463,2468,2489,2490,1876,2123,2485,2486,2124))",
          "cost_info": {
            "read_cost": "30.01",
            "eval_cost": "5.00",
            "prefix_cost": "35.01",
            "data_read_per_join": "57K"
          },
          "used_columns": [
            "variant_id",
            "position"
          ]
        }
      },
      {
        "table": {
          "table_name": "pfvd",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "test2_gaseus.pfv.variant_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 50,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "12.50",
            "eval_cost": "5.00",
            "prefix_cost": "52.51",
            "data_read_per_join": "155K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}