How do you update the Page length button caption?

Hi,

regarding this
https://datatables.net/extensions/buttons/examples/initialisation/pageLength.html

How can you update the button caption?
I tried both
"lengthMenu": [
[10,20,50,100,200,400],
[10,20,50,100,200,400]
],
"sLengthMenu": "MENU",
and
"lengthMenu": 'Display <select>'+
'<option value="10">10</option>'+
'<option value="20">20</option>'+
'<option value="30">30</option>'+
'<option value="40">40</option>'+
'<option value="50">50</option>'+
'<option value="-1">All</option>'+
'</select> records'

The first worked button-wise, but the caption didn't changed (showed "Show 10 rows").
The second just didn't worked.

Thanks,
Yishay