SELECT 
  ab__dotd.*, 
  ab__dotd_desc.h1, 
  ab__dotd_desc.page_title, 
  ab__dotd_desc.meta_description, 
  ab__dotd_desc.meta_keywords 
FROM 
  tmall_ab__dotd AS ab__dotd 
  LEFT JOIN tmall_ab__dotd_descriptions AS ab__dotd_desc ON ab__dotd.promotion_id = ab__dotd_desc.promotion_id 
  AND ab__dotd_desc.lang_code = 'en' 
WHERE 
  ab__dotd.promotion_id = 29

Query time 0.00987

JSON explain

{
  "query_block": {
    "select_id": 1,
    "const_condition": "1",
    "nested_loop": [
      {
        "table": {
          "table_name": "ab__dotd",
          "access_type": "const",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["promotion_id"],
          "ref": ["const"],
          "rows": 1,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "ab__dotd_desc",
          "access_type": "const",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["promotion_id", "lang_code"],
          "ref": ["const", "const"],
          "rows": 1,
          "filtered": 100
        }
      }
    ]
  }
}