I take MWE from here Sort bibliography with same author and same year (biblatex)
\documentclass{article}
\usepackage{filecontents}
\usepackage[style=authoryear,sorting=nyt]{biblatex}
\begin{filecontents}{\jobname.bib}
@BOOK{lennon1972a,
AUTHOR = "John Lennon",
TITLE = "My music",
YEAR = "1972"}
@BOOK{lennon1972b,
AUTHOR = "John Lennon",
TITLE = "More of my music",
YEAR = "1972"}
\end{filecontents}
\addbibresource{\jobname.bib}
\begin{document}
\cites{lennon1972a}{lennon1972b}
\printbibliography
\end{document}
Is it possible to change 'a'...'b' to another alphabet for a given language alphabet? Let Say to Roman numbering
EDITED:
According to answer below I changed code as folllow:
\documentclass{article}
\usepackage{filecontents}
\usepackage{fontspec}
\defaultfontfeatures{Ligatures=TeX}
\usepackage[russian]{babel}
\usepackage[style=authoryear,sorting=nyt]{biblatex}
\setmainfont{Dejavu Serif}
\begin{filecontents}{\jobname.bib}
@BOOK{lennon1972a,
AUTHOR = "John Lennon",
TITLE = "My music",
YEAR = "1972"}
@BOOK{lennon1972b,
AUTHOR = "John Lennon",
TITLE = "More of my music",
YEAR = "1972"}
\end{filecontents}
\addbibresource{\jobname.bib}
\DeclareFieldFormat{extrayear}{% = the 'a' in 'Jones 1995a'
\iffieldnums{labelyear}
{\Asbuk{#1}}
{\mkbibparens{\Asbuk{#1}}}}
\usepackage{enumitem}
% Some other packages, not needed for MWE
\AddEnumerateCounter{\Asbuk}{\@Asbuk}{Ы}
\AddEnumerateCounter{\asbuk}{\@asbuk}{ы}
\renewcommand{\theenumi}{(\Asbuk{enumi})}
\renewcommand{\labelenumi}{\Asbuk{enumi})}
\begin{document}
\begin{enumerate}
\item Item A
\item Item B
\end{enumerate}
\cites{lennon1972a}{lennon1972b}
\printbibliography
\end{document}
As you can see Russian letters are outputed for enumitems, but there is an error for biblatex part
\Romantakes a counter (name) as argument, but we need a macro that can directly take a number. That is why I used\RN. – moewe Jan 26 '16 at 17:30\russian@alph(or\russian@Alph). Try\makeatletter \DeclareFieldFormat{extrayear}{% = the 'a' in 'Jones 1995a' \iffieldnums{labelyear} {\russian@alph{#1}} {\mkbibparens{\russian@alph{#1}}}} \makeatother– moewe Jan 26 '16 at 17:35