How to mimic BibTeX change.case$ built-in command? [duplicate]

Question

Possible Duplicate:
Capitalizing strings ignoring closed class words

Neither bibtex.exe nor bibtex8.exe can handle unicoded database properly. Newrtheless some peoplу (and me too) do use these routines to compile list of references. Example of such use provides unicode-gost*.bst styles from the package GOST. These styles avoid using change.case$ primitive since it produces wrong output for Cyrillic alphabets.

Could someone direct me how to eleborate LaTeX command that would convert

"Some Paper Title" to "Some paper title"

and

"Some Paper Title on {LaTeX}" to "Some paper title on {LaTeX}"

?

Answer 1

Adapting Capitalizing strings ignoring closed class words one can try this:

\documentclass{article}
\usepackage[T2A,T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[russian,english]{babel}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand{\uncapitalize}{>{\SplitList{~}}m}{
  \UncapitalizeFirst#1\Uncapitalize\unskip
}
\ExplSyntaxOff
\def\Sentinel{\Uncapitalize}

\makeatletter
\def\Uncapitalize#1{%
  \def\next{#1}%
  \ifx\next\Sentinel
    \expandafter\unskip
  \else
    \CheckInList{#1}\space\expandafter\Uncapitalize
  \fi}
\def\UncapitalizeFirst#1{\expandafter\UC@next#1 \Uncapitalize}
\def\CheckInList#1{%
  \ifcsname List@\detokenize{#1}\endcsname
    #1%
  \else
    \expandafter\UC@next#1%
  \fi}
\def\UC@next#1{%
  \ifx#1\UTFviii@two@octets
     \expandafter\@firstoffour
  \else
    \ifx#1\UTFviii@three@octets
      \expandafter\expandafter\expandafter\@secondoffour
    \else
      \ifx#1\UTFviii@four@octets
        \expandafter\expandafter\expandafter\expandafter\expandafter
        \@thirdoffour
      \else
        \expandafter\expandafter\expandafter\expandafter\expandafter
        \expandafter\expandafter\@fourthoffour
      \fi
    \fi
  \fi
  {\UC@two}{\UC@three}{\UC@four}{\MakeLowercase}#1}
\def\UC@two#1#2#3{\MakeLowercase{#1#2#3}}
\def\UC@three#1#2#3#4{\MakeLowercase{#1#2#3#4}}
\def\UC@four#1#2#3#4#5{\MakeLowercase{#1#2#3#4#5}}
\providecommand\@firstoffour[4]{#1}
\providecommand\@secondoffour[4]{#2}
\providecommand\@thirdoffour[4]{#3}
\providecommand\@fourthoffour[4]{#4}
\makeatother

\begin{document}
\uncapitalize{Here is a List of Words École}

\selectlanguage{russian}

\uncapitalize{Москва Спасибо}
\end{document}

Unfortunately it doesn't work with commands or braced groups.