[LyX/master] Fix font substitutions of Thai documents

[Scott Kostyshak]

commit 008e1cc963b5ca54f1e71fa501ecb4b2306349ff
Author: Scott Kostyshak <skostysh at lyx.org>
Date:   Thu Aug 17 22:02:09 2023 -0400

    Fix font substitutions of Thai documents
    
    The substitutefont package is obsoleted now on TL because the
    required functionality is in the kernel. See here:
    
      https://ctan.org/pkg/substitutefont
---
 lib/languages |   20 ++++++++++++++++----
 1 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/lib/languages b/lib/languages
index 3101ee3..760a1ff 100644
--- a/lib/languages
+++ b/lib/languages
@@ -1522,11 +1522,23 @@ Language thai
 	  \DeclareRobustCommand{\copyright}{%
 	    \ifmmode{\nfss at text{\textcopyright}}\else\textcopyright\fi}
 	  \DeclareTextSymbol{\textcopyright}{LTH}{8}
+	  %
           % set up Thai fonts as substitue for the default families
-          \usepackage{substitutefont}
-          \substitutefont{LTH}{\rmdefault}{norasi}
-          \substitutefont{LTH}{\sfdefault}{garuda}
-          \substitutefont{LTH}{\ttdefault}{ttypist}
+	  % The 'substitutefont' package is obsolete now, since commands
+	  % from the LaTeX kernel can be used instead. See here:
+	  %   https://ctan.org/pkg/substitutefont
+	  %   https://www.latex-project.org/news/latex2e-news/ltnews31.pdf
+	  \providecommand\IfFormatAtLeastTF{\@ifl at t@r\fmtversion}
+	  \IfFormatAtLeastTF{2020/02/01}{%
+	    \DeclareFontFamilySubstitution{LTH}{\rmdefault}{norasi}
+	    \DeclareFontFamilySubstitution{LTH}{\sfdefault}{garuda}
+	    \DeclareFontFamilySubstitution{LTH}{\ttdefault}{ttypist}
+	  }{%
+	    \usepackage{substitutefont}
+	    \substitutefont{LTH}{\rmdefault}{norasi}
+	    \substitutefont{LTH}{\sfdefault}{garuda}
+	    \substitutefont{LTH}{\ttdefault}{ttypist}
+	  }
 	EndPostBabelPreamble
 End