I just found a solution to the last question:

\defineseparatorset[dashsep][][{--}]
\setuphead[section][sectionseparatorset=dashsep]

On Mon, Jan 18, 2016 at 1:01 AM, Mohammad Hossein Bateni <bateni@gmail.com>
wrote:

> Thanks, this works for figures.
>
> I couldn't get the same to work for chapters, sections, etc.
>
> \setuphead[chapter,section][conversion=lefttorightnumber]
>
> This does not have any effect.
>
>
> The solution I had in the first email of this thread (see below) has
> another issue, which I discovered later.
>
> \setuphead[chapter,title,section,subject][numbercommand=\righttoleft]
>
> The 12th section in the first chapter is written as 1.12 instead of 12.1;
> I want the latter because of r2l align.
>
> Another question: how do I change the separator to something else, say
> --?  I have played with separator and separatorset, but neither seems to
> work.
>
>
> On Sat, Jan 9, 2016 at 11:17 AM, Wolfgang Schuster <
> schuster.wolfgang@gmail.com> wrote:
>
>> Mohammad Hossein Bateni <bateni@gmail.com>
>> 3. Januar 2016 um 20:46
>> Hi,
>>
>> Again this has been partly discussed on the list and solutions were
>> already there but I didn't see anyone mention the issue with figures.
>>
>> In the following MWE we have 20 pages of a simple text with a section, a
>> footnote and a figure on each page.  The page numbers and footnote numbers
>> are fine.  Section numbers need some care to appear correctly.  I couldn't
>> figure out a similar mechanism for figure numbers, though.  The example
>> does not use Indic numbers, which does not have any effect on the problem.
>>
>>
>> \setupdirections[bidi=global,method=two]
>> \setupalign[r2l]
>>
>> %% If we don't provide the numbercommand, we'll see reverse numbering
>> starting from 10.
>> \setuphead[chapter,title,section,subject][numbercommand=\righttoleft]
>> %% The following does not accept any numbercommand but it has
>> numberconversion.
>> %% As a result figure numbers are shown in reverse.
>> \setupcaptions[numberstopper={:}]
>> %% Footnotes are fine and accept conversion.
>> %% Page numbers are also okay.
>>
>> \starttext
>>
>> \dorecurse{20}{
>>
>> \section{Test}
>> This is a very simple text.
>> And we have a footnote\footnote{Footnote text}.
>>
>> \placefigure
>> [][]
>> {Test figure.}
>> {\centerline{FIGURE BODY}}
>>
>> \page
>> }
>>
>> \stoptext
>>
>> You can use processors.
>>
>> \setupalign[righttoleft]
>>
>> \defineprocessor [lefttoright][style=\lefttoright]
>> \defineconversionset[lefttorightnumber][][lefttoright->n]
>>
>> \setupcaption[figure][numberconversionset=lefttorightnumber]
>>
>> \starttext
>>
>> \chapter{Chapter}
>>
>> \dorecurse{20}{\placefigure{Dummy
>> figure}{\blackrule[width=8cm,height=2cm]}}
>>
>> \stoptext
>>
>> Wolfgang
>>
>>
>> ___________________________________________________________________________________
>> If your question is of interest to others as well, please add an entry to
>> the Wiki!
>>
>> maillist : ntg-context@ntg.nl /
>> http://www.ntg.nl/mailman/listinfo/ntg-context
>> webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
>> archive  : http://foundry.supelec.fr/projects/contextrev/
>> wiki     : http://contextgarden.net
>>
>> ___________________________________________________________________________________
>>
>
>