diff --git a/resources/function_help/json/format_number b/resources/function_help/json/format_number
index 2b11a5d3090..16e11d1ffc7 100644
--- a/resources/function_help/json/format_number
+++ b/resources/function_help/json/format_number
@@ -1,9 +1,10 @@
 {
   "name": "format_number",
   "type": "function",
-  "description": "Returns a number formatted with the locale separator for thousands. Also truncates the number to the number of supplied places.",
+  "description": "Returns a number formatted with the locale separator for thousands. Also truncates the decimal places to the number of supplied places.",
   "arguments": [ {"arg":"number","description":"number to be formatted"},
-                 {"arg":"places","description":"integer representing the number of decimal places to truncate the string to."}],
+                 {"arg":"places","description":"integer representing the number of decimal places to truncate the string to."},
+                 {"arg":"language","optional":true,"description":"language (lowercase, two- or three-letter, ISO 639 language code) used to format the number into a string"}],
   "examples": [ { "expression":"format_number(10000000.332,2)", "returns":"'10,000,000.33'"}
   ]
 }
diff --git a/src/core/expression/qgsexpressionfunction.cpp b/src/core/expression/qgsexpressionfunction.cpp
index 935dc246959..7df781317a8 100644
--- a/src/core/expression/qgsexpressionfunction.cpp
+++ b/src/core/expression/qgsexpressionfunction.cpp
@@ -4364,29 +4364,27 @@ static QVariant fcnPi( const QVariantList &values, const QgsExpressionContext *,
 
 static QVariant fcnFormatNumber( const QVariantList &values, const QgsExpressionContext *, QgsExpression *parent, const QgsExpressionNodeFunction * )
 {
-  double value = QgsExpressionUtils::getDoubleValue( values.at( 0 ), parent );
-  int places = QgsExpressionUtils::getNativeIntValue( values.at( 1 ), parent );
+  const double value = QgsExpressionUtils::getDoubleValue( values.at( 0 ), parent );
+  const int places = QgsExpressionUtils::getNativeIntValue( values.at( 1 ), parent );
+  const QString language = QgsExpressionUtils::getStringValue( values.at( 2 ), parent );
   if ( places < 0 )
   {
     parent->setEvalErrorString( QObject::tr( "Number of places must be positive" ) );
     return QVariant();
   }
-  QLocale locale = QLocale();
+
+  QLocale locale = !language.isEmpty() ? QLocale( language ) : QLocale();
   locale.setNumberOptions( locale.numberOptions() &= ~QLocale::NumberOption::OmitGroupSeparator );
   return locale.toString( value, 'f', places );
 }
 
 static QVariant fcnFormatDate( const QVariantList &values, const QgsExpressionContext *, QgsExpression *parent, const QgsExpressionNodeFunction * )
 {
-  QDateTime datetime = QgsExpressionUtils::getDateTimeValue( values.at( 0 ), parent );
-  QString format = QgsExpressionUtils::getStringValue( values.at( 1 ), parent );
-  QString language = QgsExpressionUtils::getStringValue( values.at( 2 ), parent );
+  const QDateTime datetime = QgsExpressionUtils::getDateTimeValue( values.at( 0 ), parent );
+  const QString format = QgsExpressionUtils::getStringValue( values.at( 1 ), parent );
+  const QString language = QgsExpressionUtils::getStringValue( values.at( 2 ), parent );
 
-  QLocale locale = QLocale();
-  if ( !language.isEmpty() )
-  {
-    locale = QLocale( language );
-  }
+  QLocale locale = !language.isEmpty() ? QLocale( language ) : QLocale();
   return locale.toString( datetime, format );
 }
 
@@ -5879,7 +5877,7 @@ const QList<QgsExpressionFunction *> &QgsExpression::Functions()
         << new QgsStaticExpressionFunction( QStringLiteral( "rpad" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "string" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "width" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "fill" ) ), fcnRPad, QStringLiteral( "String" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "lpad" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "string" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "width" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "fill" ) ), fcnLPad, QStringLiteral( "String" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "format" ), -1, fcnFormatString, QStringLiteral( "String" ) )
-        << new QgsStaticExpressionFunction( QStringLiteral( "format_number" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "number" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "places" ) ), fcnFormatNumber, QStringLiteral( "String" ) )
+        << new QgsStaticExpressionFunction( QStringLiteral( "format_number" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "number" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "places" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "language" ), true, QVariant() ), fcnFormatNumber, QStringLiteral( "String" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "format_date" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "datetime" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "format" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "language" ), true, QVariant() ), fcnFormatDate, QStringList() << QStringLiteral( "String" ) << QStringLiteral( "Date and Time" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "color_grayscale_average" ),  QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "color" ) ), fcnColorGrayscaleAverage, QStringLiteral( "Color" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "color_mix_rgb" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "color1" ) )
diff --git a/tests/src/core/testqgsexpression.cpp b/tests/src/core/testqgsexpression.cpp
index 3a22958900c..18f2a02620b 100644
--- a/tests/src/core/testqgsexpression.cpp
+++ b/tests/src/core/testqgsexpression.cpp
@@ -1246,6 +1246,11 @@ class TestQgsExpression: public QObject
       QTest::newRow( "format_number large" ) << "format_number(9000000.0,0)" << false << QVariant( "9,000,000" );
       QTest::newRow( "format_number many decimals" ) << "format_number(123.45600,4)" << false << QVariant( "123.4560" );
       QTest::newRow( "format_number no decimals" ) << "format_number(1999.567,0)" << false << QVariant( "2,000" );
+#if QT_VERSION >= QT_VERSION_CHECK( 5, 12, 0 )
+      QTest::newRow( "format_number language parameter" ) << "format_number(123457.00,2,'fr')" << false << QVariant( "123\u202F457,00" );
+#else
+      QTest::newRow( "format_number language parameter" ) << "format_number(123457.00,2,'fr')" << false << QVariant( "123\u00A0457,00" );
+#endif
       QTest::newRow( "lower" ) << "lower('HeLLo')" << false << QVariant( "hello" );
       QTest::newRow( "upper" ) << "upper('HeLLo')" << false << QVariant( "HELLO" );
       QTest::newRow( "length" ) << "length('HeLLo')" << false << QVariant( 5 );