I was trying to get the page numbers in Bengali Language  in LibreOffice. I've tried by enabling CTL from Tools > Options > Language Settings > Languages. Then from Tools > Options > Language Settings > Complex Text Layout > General Options, I selected Bengali (Bangladesh) from the Numerals. At this point, not only in the footer but also in the whole document, all numbers changed in to Bengali. But my aim was to change the language to Bengali of the page numbers in the footer only, not the whole document.
In Addition I tried, to modify the Page Number character style, setting its CTL language to Bengali. But that did not change the footer numerals to Bengali number system at all!
To be frankly I did not find anything like this  for LibreOffice, as there is in MS Word. So, how can I change ONLY the page numbers into Bengali Language at the footer please?
Steps to reproduce:
1. Go to Menu > Insert > Fields > Others
2. Then go to Document > Page > Format
3. There it's no option for Bengali number system, or adding a custom number system
Page number is shown as 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ....
Page number should be shown as ০, ১, ২, ৩, ৪, ৫, ৬, ৭, ৮, ৯, ১০, ১১, ১২ ....
Operating System: All
Version: 220.127.116.11 release
Confirmed under Ubuntu 10.04 x86_64 using v18.104.22.168 Build ID: 0a0440ccc0227ad9829de5f46be37cfb6edcf72. Installation of bn_IN language pack and turning on CTL support does not allow selection of Bengali numerals for variables / fields.
Status set to NEW. Has probably always been this way, so version may need adjusting. This may be an enhancement request and it probably relates to more language packs / scripts than just Bengali. Summary edited for clarity.
I provide further details in an answer in the related AskLO thread: http://ask.libreoffice.org/en/question/27911/how-to-display-page-number-in-bengali-language-in-libreoffice-writer/
Thanks Owen Genat, for confirming this. Yes you are right, it should be "feature request". But I was not sure where to put such request for LO. So I reported it as a bug. Hopefully it will be resolved soon.
Thanks Adnan. Importance set to enhancement as per comment #2.