diff --git a/cmake/CheckBannedFunctions.cmake b/cmake/CheckBannedFunctions.cmake
index 2539f28b66..9580de817c 100644
--- a/cmake/CheckBannedFunctions.cmake
+++ b/cmake/CheckBannedFunctions.cmake
@@ -44,7 +44,7 @@ macro(check_banned_functions)
             # Only error if the line does not end with //format:allow (allow spaces between // and format)
             # we allow this for specific cases where the format specifier is needed because the
             # string is shown to the user and needs to be formatted in their locale e.g. error messages
-            if(line MATCHES "%\\d*\\.?\\d*[fg]" AND NOT line MATCHES "format:allow")
+            if(line MATCHES "%[0-9]*\\.?[0-9]*[fg]" AND NOT line MATCHES "format:allow")
                 message(FATAL_ERROR "Banned format specifier '%f' or '%g' found in ${file}")
             endif()
         endforeach()
diff --git a/common/page_info.cpp b/common/page_info.cpp
index d6273bacef..a4db85526f 100644
--- a/common/page_info.cpp
+++ b/common/page_info.cpp
@@ -26,6 +26,7 @@
 #include <macros.h>
 #include <eda_units.h>
 #include <richio.h>         // for OUTPUTFORMATTER and IO_ERROR
+#include <string_utils.h>
 
 
 // late arriving wxPAPER_A0, wxPAPER_A1
@@ -280,9 +281,9 @@ void PAGE_INFO::Format( OUTPUTFORMATTER* aFormatter ) const
     // Internally, the page size is in mils
     if( GetType() == PAGE_INFO::Custom )
     {
-        aFormatter->Print( " %g %g",
-                           GetWidthMils() * 25.4 / 1000.0,
-                           GetHeightMils() * 25.4 / 1000.0 );
+        aFormatter->Print( " %s %s",
+                           FormatDouble2Str( GetWidthMils() * 25.4 / 1000.0 ).c_str(),
+                           FormatDouble2Str( GetHeightMils() * 25.4 / 1000.0 ).c_str() );
     }
 
     if( !IsCustom() && IsPortrait() )
diff --git a/eeschema/erc/erc_report.cpp b/eeschema/erc/erc_report.cpp
index 425d870070..c4296fe107 100644
--- a/eeschema/erc/erc_report.cpp
+++ b/eeschema/erc/erc_report.cpp
@@ -20,6 +20,7 @@
 #include <wx/ffile.h>
 #include <wx/string.h>
 
+#include <locale_io.h>
 #include <sch_screen.h>
 #include <sch_marker.h>
 #include <schematic.h>
@@ -43,6 +44,9 @@ ERC_REPORT::ERC_REPORT( SCHEMATIC* aSchematic, EDA_UNITS aReportUnits ) :
 
 wxString ERC_REPORT::GetTextReport()
 {
+    // We need the global LOCALE_IO here in order to
+    // write the report in the c-locale.
+    LOCALE_IO      locale;
     UNITS_PROVIDER unitsProvider( schIUScale, m_reportUnits );
 
     wxString msg = wxString::Format( _( "ERC report (%s, Encoding UTF8)\n" ),
@@ -119,6 +123,10 @@ bool ERC_REPORT::WriteTextReport( const wxString& aFullFileName )
 
 bool ERC_REPORT::WriteJsonReport( const wxString& aFullFileName )
 {
+    // We need the global LOCALE_IO here in order to
+    // write the report in the c-locale.
+    LOCALE_IO locale;
+
     std::ofstream jsonFileStream( aFullFileName.fn_str() );
 
     UNITS_PROVIDER            unitsProvider( pcbIUScale, m_reportUnits );
diff --git a/eeschema/erc/erc_report.h b/eeschema/erc/erc_report.h
index fc586b3ae2..b5096abe64 100644
--- a/eeschema/erc/erc_report.h
+++ b/eeschema/erc/erc_report.h
@@ -33,7 +33,7 @@ public:
     ERC_REPORT( SCHEMATIC* aSchematic, EDA_UNITS aReportUnits );
 
     /**
-     * Returns the ERC report in "text" (human readable) format
+     * Returns the ERC report in "text" (human readable) format in the C-locale.
      *
      * @return The complete report
      */
@@ -47,7 +47,7 @@ public:
     bool WriteTextReport( const wxString& aFullFileName );
 
     /**
-     * Writes a JSON formatted ERC Report to the given file path
+     * Writes a JSON formatted ERC Report to the given file path in the c-locale
      *
      * @return True if the file write completed successfully, false otherwise
      */
diff --git a/eeschema/sch_io/kicad_sexpr/sch_io_kicad_sexpr.cpp b/eeschema/sch_io/kicad_sexpr/sch_io_kicad_sexpr.cpp
index f8ef30cc52..27d05fcb8d 100644
--- a/eeschema/sch_io/kicad_sexpr/sch_io_kicad_sexpr.cpp
+++ b/eeschema/sch_io/kicad_sexpr/sch_io_kicad_sexpr.cpp
@@ -989,11 +989,11 @@ void SCH_IO_KICAD_SEXPR::saveSheet( SCH_SHEET* aSheet, const SCH_SHEET_LIST& aSh
     stroke.SetWidth( aSheet->GetBorderWidth() );
     stroke.Format( m_out, schIUScale );
 
-    m_out->Print( "(fill (color %d %d %d %0.4f))",
+    m_out->Print( "(fill (color %d %d %d %s))",
                   KiROUND( aSheet->GetBackgroundColor().r * 255.0 ),
                   KiROUND( aSheet->GetBackgroundColor().g * 255.0 ),
                   KiROUND( aSheet->GetBackgroundColor().b * 255.0 ),
-                  aSheet->GetBackgroundColor().a );
+                  FormatDouble2Str( aSheet->GetBackgroundColor().a ).c_str() );
 
     KICAD_FORMAT::FormatUuid( m_out, aSheet->m_Uuid );
 
diff --git a/pcbnew/board_stackup_manager/board_stackup.cpp b/pcbnew/board_stackup_manager/board_stackup.cpp
index 0770dfee83..fb08d87a33 100644
--- a/pcbnew/board_stackup_manager/board_stackup.cpp
+++ b/pcbnew/board_stackup_manager/board_stackup.cpp
@@ -793,7 +793,7 @@ void BOARD_STACKUP::FormatBoardStackup( OUTPUTFORMATTER* aFormatter, const BOARD
             }
 
             if( item->HasEpsilonRValue() && item->HasMaterialValue( idx ) )
-                aFormatter->Print( "(epsilon_r %g)", item->GetEpsilonR( idx ) );
+                aFormatter->Print( "(epsilon_r %s)", FormatDouble2Str( item->GetEpsilonR( idx ) ).c_str() );
 
             if( item->HasLossTangentValue() && item->HasMaterialValue( idx ) )
             {
diff --git a/pcbnew/drc/drc_report.cpp b/pcbnew/drc/drc_report.cpp
index eb39966edc..8713457355 100644
--- a/pcbnew/drc/drc_report.cpp
+++ b/pcbnew/drc/drc_report.cpp
@@ -24,11 +24,12 @@
 #include <build_version.h>
 #include "drc_report.h"
 #include <drc/drc_item.h>
-#include <fstream>
+#include <locale_io.h>
 #include <macros.h>
 #include <json_common.h>
 #include <rc_json_schema.h>
 
+#include <fstream>
 
 DRC_REPORT::DRC_REPORT( BOARD* aBoard, EDA_UNITS aReportUnits,
                         std::shared_ptr<RC_ITEMS_PROVIDER> aMarkersProvider,
@@ -46,7 +47,10 @@ DRC_REPORT::DRC_REPORT( BOARD* aBoard, EDA_UNITS aReportUnits,
 
 bool DRC_REPORT::WriteTextReport( const wxString& aFullFileName )
 {
-    FILE* fp = wxFopen( aFullFileName, wxT( "w" ) );
+    // We need the global LOCALE_IO here in order to
+    // write the report in the c-locale.
+    LOCALE_IO locale;
+    FILE*     fp = wxFopen( aFullFileName, wxT( "w" ) );
 
     if( fp == nullptr )
         return false;
@@ -113,6 +117,9 @@ bool DRC_REPORT::WriteTextReport( const wxString& aFullFileName )
 
 bool DRC_REPORT::WriteJsonReport( const wxString& aFullFileName )
 {
+    // We need the global LOCALE_IO here in order to
+    // write the report in the c-locale.
+    LOCALE_IO     locale;
     std::ofstream jsonFileStream( aFullFileName.fn_str() );
 
     UNITS_PROVIDER            unitsProvider( pcbIUScale, m_reportUnits );
diff --git a/pcbnew/exporters/place_file_exporter.cpp b/pcbnew/exporters/place_file_exporter.cpp
index 7ba8dc7fd1..25207f3507 100644
--- a/pcbnew/exporters/place_file_exporter.cpp
+++ b/pcbnew/exporters/place_file_exporter.cpp
@@ -34,6 +34,8 @@
 #include <exporters/place_file_exporter.h>
 #include <pad.h>
 
+#include <fmt/format.h>
+
 #include <wx/dirdlg.h>
 
 class LIST_MOD      // An helper class used to build a list of useful footprints.
@@ -298,15 +300,11 @@ std::string PLACE_FILE_EXPORTER::GenReportData()
     LOCALE_IO   toggle;
 
     // Generate header file comments.)
-    char line[1024];
-    snprintf( line, sizeof(line), "## Footprint report - date %s\n",
-              TO_UTF8( GetISO8601CurrentDateTime() ) );
-    buffer += line;
+
+    buffer += fmt::format( "## Footprint report - date {}\n", TO_UTF8( GetISO8601CurrentDateTime() ) );
 
     wxString Title = GetBuildVersion();
-    snprintf( line, sizeof(line), "## Created by KiCad version %s\n",
-              TO_UTF8( Title ) );
-    buffer += line;
+    buffer += fmt::format( "## Printed by KiCad version {}\n", TO_UTF8( Title ) );
 
     buffer += unit_text;
 
@@ -316,15 +314,9 @@ std::string PLACE_FILE_EXPORTER::GenReportData()
 
     buffer += "\n$BOARD\n";
 
-    snprintf( line, sizeof(line), "upper_left_corner %9.6f %9.6f\n",
+    buffer += fmt::format( "upper_left_corner {:9.6f} {:9.6f}\n",
               bbbox.GetX() * conv_unit,
               bbbox.GetY() * conv_unit );
-    buffer += line;
-
-    snprintf( line, sizeof(line), "lower_right_corner %9.6f %9.6f\n",
-              bbbox.GetRight()  * conv_unit,
-              bbbox.GetBottom() * conv_unit );
-    buffer += line;
 
     buffer += "$EndBOARD\n\n";
 
@@ -344,13 +336,11 @@ std::string PLACE_FILE_EXPORTER::GenReportData()
         wxString ref = footprint->Reference().GetShownText( false );
         wxString value = footprint->Value().GetShownText( false );
 
-        snprintf( line, sizeof(line), "$MODULE %s\n", TO_UTF8( ref ) );
-        buffer += line;
+        buffer += fmt::format( "$MODULE {}\n", TO_UTF8( ref ) );
 
-        snprintf( line, sizeof(line), "reference %s\n", TO_UTF8( ref ) );
-        snprintf( line, sizeof(line), "value %s\n",  TO_UTF8( value ) );
-        snprintf( line, sizeof(line), "footprint %s\n", footprint->GetFPID().Format().c_str() );
-        buffer += line;
+        buffer += fmt::format( "reference {}\n", TO_UTF8( ref ) );
+        buffer += fmt::format( "value {}\n", TO_UTF8( value ) );
+        buffer += fmt::format( "footprint {}\n", footprint->GetFPID().Format().c_str() );
 
         buffer += "attribut";
 
@@ -368,11 +358,10 @@ std::string PLACE_FILE_EXPORTER::GenReportData()
         VECTOR2I footprint_pos = footprint->GetPosition();
         footprint_pos -= m_place_Offset;
 
-        snprintf( line, sizeof(line), "position %9.6f %9.6f  orientation %.2f\n",
+        buffer += fmt::format( "position {:9.6f} {:9.6f}  orientation {:.2f}\n",
                   footprint_pos.x * conv_unit,
                   footprint_pos.y * conv_unit,
                   footprint->GetOrientation().AsDegrees() );
-        buffer += line;
 
         if( footprint->GetLayer() == F_Cu )
             buffer += "layer front\n";
@@ -394,8 +383,7 @@ std::string PLACE_FILE_EXPORTER::GenReportData()
 
         for( PAD* pad : sortedPads )
         {
-            snprintf( line, sizeof(line), "$PAD \"%s\"\n", TO_UTF8( pad->GetNumber() ) );
-            buffer += line;
+            buffer += fmt::format( "$PAD \"{}\"\n", TO_UTF8( pad->GetNumber() ) );
 
             int layer = 0;
 
@@ -407,34 +395,29 @@ std::string PLACE_FILE_EXPORTER::GenReportData()
 
             // TODO(JE) padstacks
             static const char* layer_name[4] = { "nocopper", "back", "front", "both" };
-            snprintf( line, sizeof(line), "Shape %s Layer %s\n",
+            buffer += fmt::format( "Shape {} Layer {}\n",
                       TO_UTF8( pad->ShowPadShape( PADSTACK::ALL_LAYERS ) ),
                       layer_name[layer] );
-            buffer += line;
 
             VECTOR2I padPos = pad->GetFPRelativePosition();
 
-            snprintf( line, sizeof(line), "position %9.6f %9.6f  size %9.6f %9.6f  orientation %.2f\n",
+            buffer += fmt::format( "position {:9.6f} {:9.6f} size {:9.6f} {:9.6f} orientation {:.2f}\n",
                       padPos.x * conv_unit,
                       padPos.y * conv_unit,
                       pad->GetSize( PADSTACK::ALL_LAYERS ).x * conv_unit,
                       pad->GetSize( PADSTACK::ALL_LAYERS ).y * conv_unit,
-                      ( pad->GetOrientation() - footprint->GetOrientation() ).AsDegrees() );
-            buffer += line;
+                      pad->GetOrientation().AsDegrees() );
 
-            snprintf( line, sizeof(line), "drill %9.6f\n", pad->GetDrillSize().x * conv_unit );
-            buffer += line;
+            buffer += fmt::format( "drill {:9.6f}\n", pad->GetDrillSize().x * conv_unit );
 
-            snprintf( line, sizeof(line), "shape_offset %9.6f %9.6f\n",
+            buffer += fmt::format( "shape_offset {:9.6f} {:9.6f}\n",
                       pad->GetOffset( PADSTACK::ALL_LAYERS ).x * conv_unit,
                       pad->GetOffset( PADSTACK::ALL_LAYERS ).y * conv_unit );
-            buffer += line;
 
             buffer += "$EndPAD\n";
         }
 
-        snprintf( line, sizeof(line), "$EndMODULE  %s\n\n", TO_UTF8( ref ) );
-        buffer += line;
+        buffer += fmt::format( "$EndMODULE {}\n\n", TO_UTF8( ref ) );
     }
 
     // Generate EOF.
diff --git a/pcbnew/specctra_import_export/specctra.cpp b/pcbnew/specctra_import_export/specctra.cpp
index a30256093d..0c5961d00e 100644
--- a/pcbnew/specctra_import_export/specctra.cpp
+++ b/pcbnew/specctra_import_export/specctra.cpp
@@ -55,6 +55,7 @@
 
 #include <board.h>
 #include <pcb_track.h>
+#include <string_utils.h>
 
 #include "specctra.h"
 #include <macros.h>
@@ -3949,9 +3950,9 @@ void PLACE::Format( OUTPUTFORMATTER* out, int nestLevel )
 
     if( m_hasVertex )
     {
-        out->Print( 0, " %.6f %.6f", m_vertex.x, m_vertex.y );
+        out->Print( 0, " %s %s", FormatDouble2Str( m_vertex.x ).c_str(), FormatDouble2Str( m_vertex.y ).c_str() );
         out->Print( 0, " %s", GetTokenText( m_side ) );
-        out->Print( 0, " %.6f", m_rotation );
+        out->Print( 0, " %s", FormatDouble2Str( m_rotation ).c_str() );
     }
 
     const char* space = " ";    // one space, as c string.