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, 2457, 2448, 2444, 1694, 2122, 2445, 
    2290, 1660, 2344, 2345, 1902, 1992, 
    2139, 2458, 2075, 2413, 2449, 2455, 
    2452, 2456, 2350, 1972, 2443, 1995, 
    2454, 2453, 1900, 1905, 1787, 2451, 
    2000, 2447, 1904, 2460, 1462, 1705, 
    2462, 2463, 2464, 2466, 2467, 2468, 
    2465, 2469, 2424, 1712, 1836
  )

Query time 0.00071

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "50.41"
    },
    "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": 48,
          "rows_produced_per_join": 48,
          "filtered": "100.00",
          "index_condition": "(`test2_gaseus`.`pfv`.`variant_id` in (1912,2457,2448,2444,1694,2122,2445,2290,1660,2344,2345,1902,1992,2139,2458,2075,2413,2449,2455,2452,2456,2350,1972,2443,1995,2454,2453,1900,1905,1787,2451,2000,2447,1904,2460,1462,1705,2462,2463,2464,2466,2467,2468,2465,2469,2424,1712,1836))",
          "cost_info": {
            "read_cost": "28.81",
            "eval_cost": "4.80",
            "prefix_cost": "33.61",
            "data_read_per_join": "54K"
          },
          "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": 48,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "12.00",
            "eval_cost": "4.80",
            "prefix_cost": "50.41",
            "data_read_per_join": "149K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}