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 = 21 
  AND cscart_page_descriptions.lang_code = 'ru' 
  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 0.01618

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "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
        }
      }
    ]
  }
}