SELECT 
  pf.feature_id, 
  pf.company_id, 
  pf.feature_type, 
  pf.parent_id, 
  pf.display_on_product, 
  pf.display_on_catalog, 
  pf.display_on_header, 
  pf.categories_path, 
  pf.status, 
  pf.comparison, 
  pf.position, 
  pf.purpose, 
  pf.feature_style, 
  pf.filter_style, 
  pf.feature_code, 
  pfd.description, 
  pfd.lang_code, 
  pfd.prefix, 
  pfd.suffix, 
  pfd.full_description, 
  pfv.value, 
  pfv.variant_id, 
  pfv.value_int, 
  pfv.product_id 
FROM 
  cscart_product_features_values AS pfv 
  LEFT JOIN cscart_product_features AS pf ON pfv.feature_id = pf.feature_id 
  LEFT JOIN cscart_product_features_descriptions AS pfd ON pfd.feature_id = pf.feature_id 
  AND pfd.lang_code = 'en' 
WHERE 
  1 = 1 
  AND pfv.product_id IN (
    12949, 12950, 12951, 12952, 12953, 12942, 
    12943, 12944, 12945, 12946, 12947, 
    12954, 12955, 12948
  ) 
  AND pfv.lang_code = 'en' 
  AND pf.feature_code IN ('Brand', 'ISBN', 'GTIN', 'MPN')

Query time 0.00358

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "527.54"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "lang_code",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "product_id",
          "used_key_parts": [
            "product_id"
          ],
          "key_length": "3",
          "rows_examined_per_scan": 731,
          "rows_produced_per_join": 398,
          "filtered": "54.46",
          "index_condition": "(`test2_gaseus`.`pfv`.`product_id` in (12949,12950,12951,12952,12953,12942,12943,12944,12945,12946,12947,12954,12955,12948))",
          "cost_info": {
            "read_cost": "292.65",
            "eval_cost": "39.81",
            "prefix_cost": "332.46",
            "data_read_per_join": "307K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id",
            "value",
            "value_int",
            "lang_code"
          ],
          "attached_condition": "(`test2_gaseus`.`pfv`.`lang_code` = 'en')"
        }
      },
      {
        "table": {
          "table_name": "pf",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "feature_id"
          ],
          "key_length": "3",
          "ref": [
            "test2_gaseus.pfv.feature_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 159,
          "filtered": "40.00",
          "cost_info": {
            "read_cost": "99.53",
            "eval_cost": "15.92",
            "prefix_cost": "471.80",
            "data_read_per_join": "187K"
          },
          "used_columns": [
            "feature_id",
            "feature_code",
            "company_id",
            "purpose",
            "feature_style",
            "filter_style",
            "feature_type",
            "categories_path",
            "parent_id",
            "display_on_product",
            "display_on_catalog",
            "display_on_header",
            "status",
            "position",
            "comparison"
          ],
          "attached_condition": "(`test2_gaseus`.`pf`.`feature_code` in ('Brand','ISBN','GTIN','MPN'))"
        }
      },
      {
        "table": {
          "table_name": "pfd",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "feature_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "test2_gaseus.pfv.feature_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 159,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "39.81",
            "eval_cost": "15.92",
            "prefix_cost": "527.54",
            "data_read_per_join": "378K"
          },
          "used_columns": [
            "feature_id",
            "description",
            "full_description",
            "prefix",
            "suffix",
            "lang_code"
          ]
        }
      }
    ]
  }
}