Dear Hans,

Thank you for your reply.

Here is the missing MWE. (I will also try to attach it.)

% mwe
% document is an English translation of Arabic text; all annotations are in
English.
%
% concerning footnotes to Arabic text:
%   numbers in body should use Mashriki numbers (e.g. ٠١٢٣٤٥٦٧٨٩), and
appear between parenthesis
%   numbers in footer should use Arabic numbers (e.g. 0123456789), and
without parenthesis
%
% MWE uses dejavu for English and Amiri for and Arabic. Amiri is availble
at https://www.amirifont.org/

\mainlanguage[en-gb]

\setupdirections[bidi=global,method=one]

\starttypescriptcollection [amiri]

    \starttypescript [serif] [amiri]
        \definefontsynonym [Serif] [file:Amiri-Regular.ttf]
[features=arabic]
    \stoptypescript

    \starttypescript [amiri]
       \definetypeface [amiri] [rm] [serif] [amiri] [default]
[fallbacks=latin-fallback]
    \stoptypescript

\stoptypescriptcollection

\define\setarabic{
  \setupalign[r2l] \righttoleft \switchtobodyfont[amiri]
}

\define\setlatin{
  \setupalign[l2r] \lefttoright \switchtobodyfont[dejavu]
}


\setupnotes[footnote][]
\setupnotes[arfootnote][]

\definenote[arfootnote][footnote]
\setupnotation
    [arfootnote]
    [before=\setlatin,
     alternative=text,
    ]

\setupnote
    [arfootnote]
    [headstyle={\switchtobodyfont[amiri]},
     textcommand=\footnotenotenumbercommand,
     alternative=text,
     ]

\protected\def\footnotenotenumbercommand#1{{\high{({\convertnumber{arabicdecimals}{#1}})}}}
% unexpected results
%
\protected\def\footnotenotenumbercommand#1{{\high{({\convertnumber{abjadnumerals}{#1}})}}}
%
\protected\def\footnotenotenumbercommand#1{{\high{({\convertnumber{default}{#1}})}}}
%
% `\detokenize' variations, for comparison...
%
%
\protected\def\footnotenotenumbercommand#1{{\high{(\detokenize{\convertnumber{arabicdecimals}{#1}})}}}
%
\protected\def\footnotenotenumbercommand#1{{\high{(\detokenize{\convertnumber{abjadnumerals}{#1}})}}}
%
\protected\def\footnotenotenumbercommand#1{{\high{(\detokenize{\convertnumber{default}{#1}})}}}

\setupbodyfont[dejavu,11pt]

\starttext
\setarabic

مرحبًا\arfootnote{Annotation text.} % expected footnote `(١)`, got `1arabic`

مرحبًا\arfootnote{Annotation text.} % expected footnote `(٢)`, got `2arabic`


\stoptext

%%% end of mwe

Thanks,
Musa