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 (
    1859, 1858, 1857, 1856, 1855, 1854, 1853, 
    1852, 1851, 1850, 3929, 3924, 3928, 
    3927, 3926, 3925, 4229, 4228, 4608, 
    4606, 5648, 5649, 5650, 6213, 6214, 
    6215, 6216, 6217, 6218
  )

Query time 0.00092

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "30.46"
    },
    "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": 29,
          "rows_produced_per_join": 29,
          "filtered": "100.00",
          "index_condition": "(`cscartdb`.`pfv`.`variant_id` in (1859,1858,1857,1856,1855,1854,1853,1852,1851,1850,3929,3924,3928,3927,3926,3925,4229,4228,4608,4606,5648,5649,5650,6213,6214,6215,6216,6217,6218))",
          "cost_info": {
            "read_cost": "17.41",
            "eval_cost": "2.90",
            "prefix_cost": "20.31",
            "data_read_per_join": "33K"
          },
          "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": [
            "cscartdb.pfv.variant_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 29,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "7.25",
            "eval_cost": "2.90",
            "prefix_cost": "30.46",
            "data_read_per_join": "87K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}