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 (278, 279, 280, 281, 282, 283, 284) 
  AND pfv.lang_code = 'en' 
  AND pf.feature_code IN ('Brand', 'ISBN', 'GTIN', 'MPN')

Query time 0.00034

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.076546238,
    "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",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "loops": 1,
          "rows": 28,
          "cost": 0.04995928,
          "filtered": 49.808815,
          "index_condition": "pfv.product_id in (278,279,280,281,282,283,284) and pfv.lang_code = 'en'"
        }
      },
      {
        "table": {
          "table_name": "pf",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["feature_id"],
          "ref": ["u985510652_ecartify_dev.pfv.feature_id"],
          "loops": 13.9464681,
          "rows": 1,
          "cost": 0.013293479,
          "filtered": 100,
          "attached_condition": "pf.feature_code in ('Brand','ISBN','GTIN','MPN')"
        }
      },
      {
        "table": {
          "table_name": "pfd",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["feature_id", "lang_code"],
          "ref": ["u985510652_ecartify_dev.pfv.feature_id", "const"],
          "loops": 13.9464681,
          "rows": 1,
          "cost": 0.013293479,
          "filtered": 100,
          "attached_condition": "trigcond(pfd.lang_code = 'en')"
        }
      }
    ]
  }
}