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 (
    1912, 1904, 2443, 2444, 1705, 2462, 2463, 
    2290, 1660, 2344, 2350, 2451, 2464, 
    2466, 2467, 2468, 1905, 2465, 1900, 
    2448, 2469, 2455
  )

Query time 0.00067

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "23.11"
    },
    "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": 22,
          "rows_produced_per_join": 22,
          "filtered": "100.00",
          "index_condition": "(`test2_gaseus`.`pfv`.`variant_id` in (1912,1904,2443,2444,1705,2462,2463,2290,1660,2344,2350,2451,2464,2466,2467,2468,1905,2465,1900,2448,2469,2455))",
          "cost_info": {
            "read_cost": "13.21",
            "eval_cost": "2.20",
            "prefix_cost": "15.41",
            "data_read_per_join": "25K"
          },
          "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": 22,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "5.50",
            "eval_cost": "2.20",
            "prefix_cost": "23.11",
            "data_read_per_join": "68K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}