SELECT 
  pfvd.variant 
FROM 
  cscart_product_features_values pfv 
  INNER JOIN cscart_product_features_descriptions pfd ON pfd.feature_id = pfv.feature_id 
  AND pfd.lang_code = 'ar' 
  INNER JOIN cscart_product_feature_variant_descriptions pfvd ON pfvd.variant_id = pfv.variant_id 
  AND pfvd.lang_code = 'ar' 
WHERE 
  pfv.product_id = 425057 
  AND pfd.description = 'Warranty' 
LIMIT 
  1

Query time 0.00029

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.005219885,
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "variant_id",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "product_id",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "ref": ["const"],
          "loops": 1,
          "rows": 1,
          "cost": 0.001792605,
          "filtered": 100,
          "using_index": true
        }
      },
      {
        "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.pfv.feature_id", "const"],
          "loops": 1,
          "rows": 1,
          "cost": 0.00171364,
          "filtered": 100,
          "attached_condition": "pfd.description = 'Warranty' and pfd.lang_code = 'ar'"
        }
      },
      {
        "table": {
          "table_name": "pfvd",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["variant_id", "lang_code"],
          "ref": ["u985510652_ecartify.pfv.variant_id", "const"],
          "loops": 1,
          "rows": 1,
          "cost": 0.00171364,
          "filtered": 100,
          "attached_condition": "pfvd.lang_code = 'ar'"
        }
      }
    ]
  }
}