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, 1904, 2497, 2501, 1803, 2513, 2031, 
    1659, 1660, 2348, 2345, 2369, 2373, 
    1899, 1900, 1787, 2499, 1789, 1905, 
    2515, 2032, 2451, 2518, 2517, 2057, 
    2521, 2000, 2504, 2413, 2003, 1680, 
    2536
  )

Query time 0.00074

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "33.61"
    },
    "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": 32,
          "rows_produced_per_join": 32,
          "filtered": "100.00",
          "index_condition": "(`test2_gaseus`.`pfv`.`variant_id` in (1973,1904,2497,2501,1803,2513,2031,1659,1660,2348,2345,2369,2373,1899,1900,1787,2499,1789,1905,2515,2032,2451,2518,2517,2057,2521,2000,2504,2413,2003,1680,2536))",
          "cost_info": {
            "read_cost": "19.21",
            "eval_cost": "3.20",
            "prefix_cost": "22.41",
            "data_read_per_join": "36K"
          },
          "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": 32,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "8.00",
            "eval_cost": "3.20",
            "prefix_cost": "33.61",
            "data_read_per_join": "99K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}