diff --git a/toonz/sources/common/tgeometry/tcurveutil.cpp b/toonz/sources/common/tgeometry/tcurveutil.cpp
index 42c7bbc4..494929ae 100644
--- a/toonz/sources/common/tgeometry/tcurveutil.cpp
+++ b/toonz/sources/common/tgeometry/tcurveutil.cpp
@@ -472,7 +472,7 @@ double tdistance(const TSegment &segment, const TPointD &point) {
 
 //-----------------------------------------------------------------------------
 /*
-This formule is derived from Graphic Gems pag. 600
+This formula is derived from Graphic Gems pag. 600
 
   e = h^2 |a|/8
 
diff --git a/toonz/sources/common/tvectorimage/outlineApproximation.cpp b/toonz/sources/common/tvectorimage/outlineApproximation.cpp
index 9ab70b01..ce0727e8 100644
--- a/toonz/sources/common/tvectorimage/outlineApproximation.cpp
+++ b/toonz/sources/common/tvectorimage/outlineApproximation.cpp
@@ -35,7 +35,7 @@ class notValidOutline {};
 namespace {
 
 /*
-  This formule is derived from Graphic Gems pag. 600
+  This formula is derived from Graphic Gems pag. 600
 
     e = h^2 |a|/8
 
diff --git a/toonz/sources/common/tvrender/tfont_qt.cpp b/toonz/sources/common/tvrender/tfont_qt.cpp
index cd79eb5f..83ef8ae7 100644
--- a/toonz/sources/common/tvrender/tfont_qt.cpp
+++ b/toonz/sources/common/tvrender/tfont_qt.cpp
@@ -176,8 +176,8 @@ TPoint TFont::drawChar(QImage &outImage, TPoint &unused, wchar_t charcode,
   // alphaMapForGlyph with a space character returns an invalid
   // QImage for some reason.
   // Bug 3604: https://github.com/opentoonz/opentoonz/issues/3604
-  // (21/1/2022) Use this workaround for all platforms as the crash also occured
-  // in windows when the display is scaled up.
+  // (21/1/2022) Use this workaround for all platforms as the crash also
+  // occurred in windows when the display is scaled up.
   if (chars[0].isSpace()) {
 #if QT_VERSION >= QT_VERSION_CHECK(5, 11, 0)
     int w = QFontMetrics(m_pimpl->m_font).horizontalAdvance(chars[0]);
diff --git a/toonz/sources/include/tregion.h b/toonz/sources/include/tregion.h
index f2ae4c9e..24cb5348 100644
--- a/toonz/sources/include/tregion.h
+++ b/toonz/sources/include/tregion.h
@@ -244,7 +244,7 @@ public:
 };
 
 //-----------------------------------------------------------------------------
-/*Spostata in tregion.cpp
+/* Moved to tregion.cpp
 inline int TRegion::getStyle() const
 {
 int ret = 0;
@@ -271,10 +271,10 @@ public:
   virtual void update(const TPointD &p1, const TPointD &p2) = 0;
 };
 
-// permette di calcolare varie grandesse sul poligono della regione,
-// come l'area, il baricentro, il perimetro...
-// per usarla si deve sottoclassare la classe virtuale TRegionFeatureFormula
-// specificando la formual della grandezza da calcolare.
+// allows to calculate various magnitudes on the polygon of the region,
+// such as area, center of gravity, perimeter etc...
+// to use it, subclass the virtual class TRegionFeatureFormula
+// specifying the formula of the quantity to calculate.
 
 void DVAPI computeRegionFeature(const TRegion &r,
                                 TRegionFeatureFormula &formula);
diff --git a/toonz/sources/include/tsound_t.h b/toonz/sources/include/tsound_t.h
index beedfb22..72ad6cf2 100644
--- a/toonz/sources/include/tsound_t.h
+++ b/toonz/sources/include/tsound_t.h
@@ -139,7 +139,7 @@ from which it's created. It has no reference to the object.
 
   //----------------------------------------------------------------------------
 
-  //! Applies a transformation (echo, reverb, ect) to the object and returns the
+  //! Applies a transformation (echo, reverb, etc) to the object and returns the
   //! transformed soundtrack
   TSoundTrackP apply(TSoundTransform *transform) override;
   //----------------------------------------------------------------------------
diff --git a/toonz/sources/include/tspectrum.h b/toonz/sources/include/tspectrum.h
index 6e350fa3..f48174a0 100644
--- a/toonz/sources/include/tspectrum.h
+++ b/toonz/sources/include/tspectrum.h
@@ -41,7 +41,7 @@ private:
                          ColorKey(s, T()),
                          [](const ColorKey &a, const ColorKey &b) {
                            return a.first < b.first;
-                         });  // compare only key postions
+                         });  // compare only key positions
 
     if (b == m_sortedKeys.end())
       return m_sortedKeys.rbegin()->second;
diff --git a/toonz/sources/tnztools/toolutils.cpp b/toonz/sources/tnztools/toolutils.cpp
index facbaa97..e41187a3 100644
--- a/toonz/sources/tnztools/toolutils.cpp
+++ b/toonz/sources/tnztools/toolutils.cpp
@@ -1490,7 +1490,7 @@ double ToolUtils::ConeSubVolume::compute(double cover) {
   if (i == 20)
     return m_values[i];
   else
-    // Interpolazione lineare.
+    // Linear interpolation.
     return (-(x - (i + 1)) * m_values[i]) - (-(x - i) * m_values[i + 1]);
 }
 
@@ -1612,14 +1612,14 @@ void ToolUtils::drawBalloon(const TPointD &pos, std::string text,
   pp.moveTo(x0, y - 8 * devPixRatio);
   pp.lineTo(0, y + delta.y);
   pp.lineTo(x0, y);
-  /* bordi arrotondati
+  /* rounded borders
   int arcSize = 10;
   pp.arcTo(x0,y1-arcSize,arcSize,arcSize,180,90);
   pp.arcTo(x1-arcSize,y1-arcSize,arcSize,arcSize,270,90);
   pp.arcTo(x1-arcSize,y0,arcSize,arcSize,0,90);
   pp.arcTo(x0,y0,arcSize,arcSize,90,90);
   */
-  // bordi acuti
+  // sharp edges
   pp.lineTo(x0, y1);
   pp.lineTo(x1, y1);
   pp.lineTo(x1, y0);
diff --git a/toonz/sources/toonz/castviewer.cpp b/toonz/sources/toonz/castviewer.cpp
index 6db8ca14..139d3f82 100644
--- a/toonz/sources/toonz/castviewer.cpp
+++ b/toonz/sources/toonz/castviewer.cpp
@@ -169,7 +169,7 @@ void CastTreeViewer::enableCommands() {
 
 void CastTreeViewer::onFolderChanged(QTreeWidgetItem *current,
                                      QTreeWidgetItem *previous) {
-  // rende la selezione corrente; serve per intercettare il comando MI_Clear
+  // makes the selection current; serves to intercept the MI_Clear command
   makeCurrent();
 }
 
@@ -741,7 +741,7 @@ QMenu *CastBrowser::getContextMenu(QWidget *parent, int index) {
   for (it = indices.begin(); it != indices.end(); ++it) {
     int index = *it;
     if (index < 0 || index >= m_castItems->getItemCount())
-      continue;  // non dovrebbe mai succedere
+      continue;  // should never happen
     TXshSimpleLevel *sl = m_castItems->getItem(index)->getSimpleLevel();
     if (!sl) {
       if (m_castItems->getItem(index)->getPaletteLevel())
@@ -775,7 +775,7 @@ QMenu *CastBrowser::getContextMenu(QWidget *parent, int index) {
     menu->addAction(cm->getAction(MI_EditLevel));
   if (!paletteSelected) menu->addAction(cm->getAction(MI_SaveLevel));
   menu->addSeparator();
-  // MI_ConvertToVectors se sono stati selezionati solo livelli non vettoriali
+  // MI_ConvertToVectors if only non-vector layers were selected
   if (!audioSelected && !paletteSelected && !vectorLevelSelected)
     menu->addAction(cm->getAction(MI_ConvertToVectors));
   menu->addSeparator();
diff --git a/toonz/sources/toonz/sceneviewer.cpp b/toonz/sources/toonz/sceneviewer.cpp
index 4dbcfb0d..1900de9e 100644
--- a/toonz/sources/toonz/sceneviewer.cpp
+++ b/toonz/sources/toonz/sceneviewer.cpp
@@ -1042,7 +1042,7 @@ void SceneViewer::showEvent(QShowEvent *) {
   m_visualSettings.m_sceneProperties =
       TApp::instance()->getCurrentScene()->getScene()->getProperties();
 
-  // Se il viewer e' show e il preview e' attivo aggiungo il listner al preview
+  // If the viewer is hidden and preview is activated, remove the listener from preview
   if (m_previewMode != NO_PREVIEW)
     Previewer::instance(m_previewMode == SUBCAMERA_PREVIEW)->addListener(this);
 
@@ -1126,7 +1126,7 @@ void SceneViewer::showEvent(QShowEvent *) {
 //-----------------------------------------------------------------------------
 
 void SceneViewer::hideEvent(QHideEvent *) {
-  // Se il viewer e' hide e il preview e' attivo rimuovo il listner dal preview
+  // If the viewer is hidden and preview is activated, remove the listener from preview
   if (m_previewMode != NO_PREVIEW)
     Previewer::instance(m_previewMode == SUBCAMERA_PREVIEW)
         ->removeListener(this);