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, 2000, 2504, 2501, 2503, 2413, 2003, 
    1659, 1660, 2348, 2345, 2369, 2373, 
    2370, 2374, 1680, 1787, 2497, 1803, 
    2123, 1721, 1900, 1899, 1904, 1905, 
    1789, 2499, 2508, 2124, 1723, 2513, 
    2031, 2515, 2032, 2451, 2518, 2517, 
    2057, 2521, 2524, 2122, 2043, 2121, 
    1727, 1879, 2536
  )

Query time 0.00092

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "48.31"
    },
    "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": 46,
          "rows_produced_per_join": 46,
          "filtered": "100.00",
          "index_condition": "(`test2_gaseus`.`pfv`.`variant_id` in (1973,2000,2504,2501,2503,2413,2003,1659,1660,2348,2345,2369,2373,2370,2374,1680,1787,2497,1803,2123,1721,1900,1899,1904,1905,1789,2499,2508,2124,1723,2513,2031,2515,2032,2451,2518,2517,2057,2521,2524,2122,2043,2121,1727,1879,2536))",
          "cost_info": {
            "read_cost": "27.61",
            "eval_cost": "4.60",
            "prefix_cost": "32.21",
            "data_read_per_join": "52K"
          },
          "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": 46,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "11.50",
            "eval_cost": "4.60",
            "prefix_cost": "48.31",
            "data_read_per_join": "143K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}