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 (
    12444, 25125, 58069, 47878, 62258, 58084, 
    10348, 58096, 62259, 62294, 19150, 
    21901, 62293, 62292, 58116, 22195, 
    19049, 12412, 21907
  )

Query time 0.00067

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "15.28"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "variant_feature_idx",
            "idx_var_feat_pos"
          ],
          "key": "idx_var_feat_pos",
          "used_key_parts": [
            "variant_id"
          ],
          "key_length": "3",
          "rows_examined_per_scan": 19,
          "rows_produced_per_join": 19,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "2.53",
            "eval_cost": "1.90",
            "prefix_cost": "4.43",
            "data_read_per_join": "21K"
          },
          "used_columns": [
            "variant_id",
            "position"
          ],
          "attached_condition": "(`cscart_db`.`pfv`.`variant_id` in (12444,25125,58069,47878,62258,58084,10348,58096,62259,62294,19150,21901,62293,62292,58116,22195,19049,12412,21907))"
        }
      },
      {
        "table": {
          "table_name": "pfvd",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "cscart_db.pfv.variant_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 19,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "8.95",
            "eval_cost": "1.90",
            "prefix_cost": "15.28",
            "data_read_per_join": "142K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}