SELECT 
  v.product_id, 
  v.feature_id, 
  v.value, 
  v.value_int, 
  v.variant_id, 
  f.feature_type, 
  fd.description, 
  fd.prefix, 
  fd.suffix, 
  vd.variant, 
  f.parent_id, 
  f.position, 
  gf.position as gposition 
FROM 
  cscart_product_features as f 
  LEFT JOIN cscart_product_features_values as v ON v.feature_id = f.feature_id 
  LEFT JOIN cscart_product_features_descriptions as fd ON fd.feature_id = v.feature_id 
  AND fd.lang_code = 'de' 
  LEFT JOIN cscart_product_feature_variants fv ON fv.variant_id = v.variant_id 
  LEFT JOIN cscart_product_feature_variant_descriptions as vd ON vd.variant_id = fv.variant_id 
  AND vd.lang_code = 'de' 
  LEFT JOIN cscart_product_features as gf ON gf.feature_id = f.parent_id 
  AND gf.feature_type = 'G' 
WHERE 
  f.status IN ('A') 
  AND v.product_id in (137) 
  AND f.display_on_catalog = 'Y' 
  AND (
    f.categories_path = '' 
    OR FIND_IN_SET(43213, f.categories_path)
  ) 
  AND IF(
    f.parent_id, 
    (
      SELECT 
        status 
      FROM 
        cscart_product_features as df 
      WHERE 
        df.feature_id = f.parent_id
    ), 
    'A'
  ) IN ('A') 
  AND (
    v.variant_id != 0 
    OR (
      f.feature_type != 'C' 
      AND v.value != ''
    ) 
    OR (f.feature_type = 'C') 
    OR v.value_int != ''
  ) 
  AND v.lang_code = 'de' 
ORDER BY 
  fd.description, 
  fv.position

Query time 0.00049

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.056980809,
    "filesort": {
      "sort_key": "fd.description, fv.position",
      "temporary_table": {
        "nested_loop": [
          {
            "table": {
              "table_name": "v",
              "access_type": "ref",
              "possible_keys": [
                "PRIMARY",
                "fl",
                "variant_id",
                "lang_code",
                "product_id",
                "fpl",
                "idx_product_feature_variant_id"
              ],
              "key": "idx_product_feature_variant_id",
              "key_length": "3",
              "used_key_parts": ["product_id"],
              "ref": ["const"],
              "loops": 1,
              "rows": 9,
              "cost": 0.011895363,
              "filtered": 54.22251892,
              "index_condition": "v.lang_code = 'de'"
            }
          },
          {
            "table": {
              "table_name": "f",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY", "status"],
              "key": "PRIMARY",
              "key_length": "3",
              "used_key_parts": ["feature_id"],
              "ref": ["cscart.v.feature_id"],
              "loops": 4.88002681,
              "rows": 1,
              "cost": 0.008642493,
              "filtered": 99.64788818,
              "attached_condition": "f.`status` = 'A' and f.display_on_catalog = 'Y' and (f.categories_path = '' or find_in_set(43213,f.categories_path)) and if(f.parent_id,(subquery#2),'A') = 'A' and (v.variant_id <> 0 or f.feature_type <> 'C' and v.`value` <> '' or f.feature_type = 'C' or v.value_int <> '')"
            }
          },
          {
            "table": {
              "table_name": "fd",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY"],
              "key": "PRIMARY",
              "key_length": "9",
              "used_key_parts": ["feature_id", "lang_code"],
              "ref": ["cscart.v.feature_id", "const"],
              "loops": 4.862843617,
              "rows": 1,
              "cost": 0.009022383,
              "filtered": 100,
              "attached_condition": "trigcond(fd.lang_code = 'de')"
            }
          },
          {
            "table": {
              "table_name": "fv",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY"],
              "key": "PRIMARY",
              "key_length": "3",
              "used_key_parts": ["variant_id"],
              "ref": ["cscart.v.variant_id"],
              "loops": 4.862843617,
              "rows": 1,
              "cost": 0.009403893,
              "filtered": 100
            }
          },
          {
            "table": {
              "table_name": "vd",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY"],
              "key": "PRIMARY",
              "key_length": "9",
              "used_key_parts": ["variant_id", "lang_code"],
              "ref": ["cscart.fv.variant_id", "const"],
              "loops": 4.862843617,
              "rows": 1,
              "cost": 0.009403893,
              "filtered": 100,
              "attached_condition": "trigcond(vd.lang_code = 'de' and trigcond(fv.variant_id is not null))"
            }
          },
          {
            "table": {
              "table_name": "gf",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY"],
              "key": "PRIMARY",
              "key_length": "3",
              "used_key_parts": ["feature_id"],
              "ref": ["cscart.f.parent_id"],
              "loops": 4.862843617,
              "rows": 1,
              "cost": 0.008612783,
              "filtered": 100,
              "attached_condition": "trigcond(gf.feature_type = 'G')"
            }
          }
        ],
        "subqueries": [
          {
            "expression_cache": {
              "state": "uninitialized",
              "query_block": {
                "select_id": 2,
                "cost": 0.001933826,
                "nested_loop": [
                  {
                    "table": {
                      "table_name": "df",
                      "access_type": "eq_ref",
                      "possible_keys": ["PRIMARY"],
                      "key": "PRIMARY",
                      "key_length": "3",
                      "used_key_parts": ["feature_id"],
                      "ref": ["cscart.f.parent_id"],
                      "loops": 1,
                      "rows": 1,
                      "cost": 0.001933826,
                      "filtered": 100
                    }
                  }
                ]
              }
            }
          }
        ]
      }
    }
  }
}