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, 2143, 1954, 1660, 2132, 2131, 
    2415, 2413, 1705, 2290, 1836, 1973, 
    1789, 2497, 2541, 2122, 2043, 1659, 
    2348, 2345, 2370, 2374, 2499, 1787, 
    1900, 1899, 1905, 1904, 2501, 2123, 
    1721
  )

Query time 0.00086

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 (1935,1803,2143,1954,1660,2132,2131,2415,2413,1705,2290,1836,1973,1789,2497,2541,2122,2043,1659,2348,2345,2370,2374,2499,1787,1900,1899,1905,1904,2501,2123,1721))",
          "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"
          ]
        }
      }
    ]
  }
}