SELECT 
  cscart_pages.*, 
  cscart_page_descriptions.* 
FROM 
  cscart_pages 
  INNER JOIN cscart_page_descriptions ON cscart_pages.page_id = cscart_page_descriptions.page_id 
WHERE 
  cscart_pages.page_id = 20 
  AND cscart_page_descriptions.lang_code = 'ja' 
  AND (
    cscart_pages.usergroup_ids = '' 
    OR FIND_IN_SET(0, cscart_pages.usergroup_ids) 
    OR FIND_IN_SET(1, cscart_pages.usergroup_ids)
  ) 
  AND cscart_pages.page_type IN ('T', 'L', 'B', 'F')

Query time 0.00041

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_pages",
      "access_type": "const",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["page_id"],
      "ref": ["const"],
      "rows": 1,
      "filtered": 100
    },
    "table": {
      "table_name": "cscart_page_descriptions",
      "access_type": "const",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["page_id", "lang_code"],
      "ref": ["const", "const"],
      "rows": 1,
      "filtered": 100
    }
  }
}