LaTeX writer: fix bug when a language is specified in two different ways.

If you used `lang: de-DE` but then had a span or div with `lang=de`, the
preamble would try to load `ngerman` twice, leading to an error.

This fix ensures that a language is only loaded once.

Closes #9472.

2 files changed, 90 insertions, 3 deletions

diff --git a/src/Text/Pandoc/Writers/LaTeX.hs b/src/Text/Pandoc/Writers/LaTeX.hs
index 9eb7be4f6..2c3404310 100644
--- a/src/Text/Pandoc/Writers/LaTeX.hs
+++ b/src/Text/Pandoc/Writers/LaTeX.hs
@@ -175,7 +175,6 @@ pandocToLaTeX options (Pandoc meta blocks) = do
   titleMeta <- stringToLaTeX TextString $ stringify $ docTitle meta
   authorsMeta <- mapM (stringToLaTeX TextString . stringify) $ docAuthors meta
   -- we need a default here since lang is used in template conditionals
-  let otherLangs = [l | l <- docLangs, mblang /= Just l]
   let hasStringValue x = isJust (getField x metadata :: Maybe (Doc Text))
   let geometryFromMargins = mconcat $ intersperse ("," :: Doc Text) $
                             mapMaybe (\(x,y) ->
@@ -251,15 +250,18 @@ pandocToLaTeX options (Pandoc meta blocks) = do
                           -> resetField "papersize" ("a" <> ds)
                       _   -> id)
                   metadata
+  let babelLang = mblang >>= toBabel
   let context' =
           -- note: lang is used in some conditionals in the template,
           -- so we need to set it if we have any babel/polyglossia:
           maybe id (\l -> defField "lang"
                       (literal $ renderLang l)) mblang
         $ maybe id (\l -> defField "babel-lang"
-                      (literal l)) (mblang >>= toBabel)
+                      (literal l)) babelLang
         $ defField "babel-otherlangs"
-             (map literal $ mapMaybe toBabel otherLangs)
+             (map literal
+               (nubOrd . catMaybes . filter (/= babelLang)
+                $ map toBabel docLangs))
         $ defField "latex-dir-rtl"
            ((render Nothing <$> getField "dir" context) ==
                Just ("rtl" :: Text)) context
diff --git a/test/command/9472.md b/test/command/9472.md
new file mode 100644
index 000000000..48fec385d
--- /dev/null
+++ b/test/command/9472.md
@@ -0,0 +1,85 @@
+```
+% pandoc -t latex -s
+---
+lang: de-DE
+---
+
+More text in English. ['Zitat auf Deutsch.']{lang=de}
+
+[Bonjour]{lang=fr} [café]{lang="fr-FR"}
+^D
+% Options for packages loaded elsewhere
+\PassOptionsToPackage{unicode}{hyperref}
+\PassOptionsToPackage{hyphens}{url}
+%
+\documentclass[
+]{article}
+\usepackage{amsmath,amssymb}
+\usepackage{iftex}
+\ifPDFTeX
+  \usepackage[T1]{fontenc}
+  \usepackage[utf8]{inputenc}
+  \usepackage{textcomp} % provide euro and other symbols
+\else % if luatex or xetex
+  \usepackage{unicode-math} % this also loads fontspec
+  \defaultfontfeatures{Scale=MatchLowercase}
+  \defaultfontfeatures[\rmfamily]{Ligatures=TeX,Scale=1}
+\fi
+\usepackage{lmodern}
+\ifPDFTeX\else
+  % xetex/luatex font selection
+\fi
+% Use upquote if available, for straight quotes in verbatim environments
+\IfFileExists{upquote.sty}{\usepackage{upquote}}{}
+\IfFileExists{microtype.sty}{% use microtype if available
+  \usepackage[]{microtype}
+  \UseMicrotypeSet[protrusion]{basicmath} % disable protrusion for tt fonts
+}{}
+\makeatletter
+\@ifundefined{KOMAClassName}{% if non-KOMA class
+  \IfFileExists{parskip.sty}{%
+    \usepackage{parskip}
+  }{% else
+    \setlength{\parindent}{0pt}
+    \setlength{\parskip}{6pt plus 2pt minus 1pt}}
+}{% if KOMA class
+  \KOMAoptions{parskip=half}}
+\makeatother
+\usepackage{xcolor}
+\setlength{\emergencystretch}{3em} % prevent overfull lines
+\providecommand{\tightlist}{%
+  \setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}
+\setcounter{secnumdepth}{-\maxdimen} % remove section numbering
+\ifLuaTeX
+\usepackage[bidi=basic]{babel}
+\else
+\usepackage[bidi=default]{babel}
+\fi
+\babelprovide[main,import]{ngerman}
+\babelprovide[import]{french}
+% get rid of language-specific shorthands (see #6817):
+\let\LanguageShortHands\languageshorthands
+\def\languageshorthands#1{}
+\ifLuaTeX
+  \usepackage{selnolig}  % disable illegal ligatures
+\fi
+\usepackage{bookmark}
+\IfFileExists{xurl.sty}{\usepackage{xurl}}{} % add URL line breaks if available
+\urlstyle{same}
+\hypersetup{
+  pdflang={de-DE},
+  hidelinks,
+  pdfcreator={LaTeX via pandoc}}
+
+\author{}
+\date{}
+
+\begin{document}
+
+More text in English. \foreignlanguage{ngerman}{`Zitat auf Deutsch.'}
+
+\foreignlanguage{french}{Bonjour} \foreignlanguage{french}{café}
+
+\end{document}
+
+```