SELECT 
  * 
FROM 
  cscart_bm_locations as l 
  LEFT JOIN cscart_bm_locations_descriptions as d ON d.location_id = l.location_id 
  AND d.lang_code = 'en' 
WHERE 
  l.layout_id = 3 
  AND l.is_default = 1 
ORDER BY 
  l.is_default desc

Query time 0.00860

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "l",
          "access_type": "ALL",
          "rows": 79,
          "filtered": 100,
          "attached_condition": "l.layout_id = 3 and l.is_default = 1"
        }
      },
      {
        "table": {
          "table_name": "d",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "12",
          "used_key_parts": ["location_id", "lang_code"],
          "ref": ["dev_db.l.location_id", "const"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "trigcond(d.location_id = l.location_id and d.lang_code = 'en')"
        }
      }
    ]
  }
}