SELECT 
  ab__dotd.*, 
  ab__dotd_desc.h1, 
  ab__dotd_desc.page_title, 
  ab__dotd_desc.meta_description, 
  ab__dotd_desc.meta_keywords 
FROM 
  cscart_ab__dotd AS ab__dotd 
  LEFT JOIN cscart_ab__dotd_descriptions AS ab__dotd_desc ON ab__dotd.promotion_id = ab__dotd_desc.promotion_id 
  AND ab__dotd_desc.lang_code = 'ru' 
WHERE 
  ab__dotd.promotion_id = 25

Query time 0.00037

JSON explain

{
  "query_block": {
    "select_id": 1,
    "const_condition": "1",
    "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
    }
  }
}