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 (
    1935, 1803, 2421, 1836, 1660, 1705, 2413, 
    1954, 2415, 2419, 2420, 2290, 2143, 
    2132, 2131, 1712, 1973, 1904, 2497, 
    2524, 2122, 2043, 1659, 2348, 2345, 
    2369, 2373, 1905, 1789, 2499, 1787, 
    1900, 1899, 2501, 2123, 1721, 2124, 
    1723, 2121, 1727, 2451, 1879, 2513, 
    2031, 2515, 2032, 2518, 2517, 2057, 
    2521, 2000, 2504, 2003, 1680, 2536, 
    1912, 2378
  )

Query time 0.00071

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "59.86"
    },
    "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": 57,
          "rows_produced_per_join": 57,
          "filtered": "100.00",
          "index_condition": "(`test2_gaseus`.`pfv`.`variant_id` in (1935,1803,2421,1836,1660,1705,2413,1954,2415,2419,2420,2290,2143,2132,2131,1712,1973,1904,2497,2524,2122,2043,1659,2348,2345,2369,2373,1905,1789,2499,1787,1900,1899,2501,2123,1721,2124,1723,2121,1727,2451,1879,2513,2031,2515,2032,2518,2517,2057,2521,2000,2504,2003,1680,2536,1912,2378))",
          "cost_info": {
            "read_cost": "34.21",
            "eval_cost": "5.70",
            "prefix_cost": "39.91",
            "data_read_per_join": "65K"
          },
          "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": 57,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "14.25",
            "eval_cost": "5.70",
            "prefix_cost": "59.86",
            "data_read_per_join": "177K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}