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 (
    1660, 1900, 1659, 1876, 2123, 1973, 2489, 
    2490, 2344, 2345, 1905, 2485, 2486, 
    1787, 2451, 1904, 2124, 2369, 2373, 
    2000, 2503, 2413, 2003, 2504, 2501, 
    2348, 2370, 2374, 1680, 1803, 1721, 
    2497, 1899, 1789, 2499, 1723, 2508, 
    2513, 2031, 2515, 2032, 2517, 2057, 
    2518, 2521
  )

Query time 0.00081

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "47.26"
    },
    "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": 45,
          "rows_produced_per_join": 45,
          "filtered": "100.00",
          "index_condition": "(`gaseus`.`pfv`.`variant_id` in (1660,1900,1659,1876,2123,1973,2489,2490,2344,2345,1905,2485,2486,1787,2451,1904,2124,2369,2373,2000,2503,2413,2003,2504,2501,2348,2370,2374,1680,1803,1721,2497,1899,1789,2499,1723,2508,2513,2031,2515,2032,2517,2057,2518,2521))",
          "cost_info": {
            "read_cost": "27.01",
            "eval_cost": "4.50",
            "prefix_cost": "31.51",
            "data_read_per_join": "51K"
          },
          "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": [
            "gaseus.pfv.variant_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 45,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "11.25",
            "eval_cost": "4.50",
            "prefix_cost": "47.26",
            "data_read_per_join": "140K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}