% This file is embedded in datatool-user.pdf version 3.0.1 2025-03-05
% Example 11 IJ-Initial Support
% Label: "ex:ijinitial"
% arara: pdflatex
% arara: pdfcrop
\documentclass[12pt]{article}
\pagestyle{empty}
\usepackage{datatool-base}
\ExplSyntaxOn
 \newcommand{\DTLdutchLocaleGetInitialLetter}[2]{
 \tl_clear:N #2
 \text_map_inline:nn { #1 } 
 { 
 \tl_if_empty:NTF #2 
  {
    \datatool_if_letter:nT { ##1 }
    {
      \tl_set:Nn #2 { ##1 }
      \tl_if_in:nnF { Ii } { ##1 } { \text_map_break: } 
    }
  } 
 {
  \tl_if_in:nnT { Jj } { ##1 } 
    {
      \tl_put_right:Nn #2 { ##1 }
    }
  \text_map_break:
 }
 }
}
\ExplSyntaxOff 

\let\DTLCurrentLocaleGetInitialLetter\DTLdutchLocaleGetInitialLetter 
\begin{document}
IJsselmeer: \DTLinitials{IJsselmeer}
Industrieel: \DTLinitials{Industrieel}
``IJsselmeer'': \DTLinitials{``IJsselmeer''}
``Industrieel'': \DTLinitials{``Industrieel''} 
\end{document}