diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 61e315f..2e7b420 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -51,6 +51,7 @@ set(
 	nsSBCharSetProber.cpp
 	nsSJISProber.cpp
 	nsUTF8Prober.cpp
+	nsLanguageDetector.cpp
 	nsLatin1Prober.cpp
 	nsUniversalDetector.cpp
 	uchardet.cpp
diff --git a/src/nsLanguageDetector.cpp b/src/nsLanguageDetector.cpp
new file mode 100644
index 0000000..c952c6c
--- /dev/null
+++ b/src/nsLanguageDetector.cpp
@@ -0,0 +1,180 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is Mozilla Universal charset detector code. This
+ * file was later added by Jehan in 2021 to add language detection.
+ *
+ * The Initial Developer of the Original Code is Netscape Communications
+ * Corporation.
+ * Portions created by the Initial Developer are Copyright (C) 2001 the
+ * Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *          Jehan <zemarmot.net> (2021)
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+#include "nsLanguageDetector.h"
+
+nsDetectState nsLanguageDetector::HandleData(const int* codePoints, PRUint32 cpLen)
+{
+  int order;
+
+  for (PRUint32 i = 0; i < cpLen; i++)
+  {
+    order = GetOrderFromCodePoint(codePoints[i]);
+
+    mTotalChar++;
+#if 0
+    /* TODO: detect illegal unicode codepoints. */
+    if (order == ILL)
+    {
+      /* When encountering an illegal codepoint, no need
+       * to continue analyzing data. It means this is not right, hence
+       * that the encoding we deducted this codepoint from is wrong.
+       */
+      mState = STATE_UNLIKELY;
+      break;
+    }
+    else if (order == CTR)
+    {
+      /* TODO: also detect ctrl character, as well as symbols and
+       * punctuation, possibly return/line feeds and numbers. See how to
+       * use these to improve language detection logics.
+       * */
+      mCtrlChar++;
+    }
+#endif
+
+    /* Negative order represent non-frequent characters, yet not disqualifying.
+     * We may also have a text with a bit of foreign quotes in it or
+     * very unusual characters sometimes.
+     */
+    if (order >= 0 && order < mModel->freqCharCount)
+    {
+      mFreqChar++;
+
+      if (mLastOrder >= 0 && mLastOrder < mModel->freqCharCount)
+      {
+        mTotalSeqs++;
+        ++(mSeqCounters[mModel->precedenceMatrix[mLastOrder*mModel->freqCharCount+order]]);
+      }
+    }
+    mLastOrder = order;
+  }
+
+  if (mState == STATE_DETECTING)
+    if (mTotalSeqs > LANG_SB_ENOUGH_REL_THRESHOLD)
+    {
+      float cf = GetConfidence();
+      if (cf > LANG_POSITIVE_SHORTCUT_THRESHOLD)
+        mState = STATE_FOUND;
+      else if (cf < LANG_NEGATIVE_SHORTCUT_THRESHOLD)
+        mState = STATE_UNLIKELY;
+    }
+
+  return mState;
+}
+
+void nsLanguageDetector::Reset(void)
+{
+  mState     = STATE_DETECTING;
+  mLastOrder = -1;
+  for (PRUint32 i = 0; i < LANG_NUMBER_OF_SEQ_CAT; i++)
+    mSeqCounters[i] = 0;
+  mTotalSeqs = 0;
+  mTotalChar = 0;
+  mCtrlChar  = 0;
+  mFreqChar  = 0;
+}
+
+float nsLanguageDetector::GetConfidence(void)
+{
+  float r;
+
+  if (mTotalSeqs > 0) {
+    /* Create a "logical" number of sequences rather than real, but
+     * weighing the various sequences.
+     * Basically positive sequences will boost the confidence, probable
+     * sequence a bit, but not so much, neutral sequences will not be
+     * integrated in the confidence.
+     * Negative sequences will negatively impact the confidence as much
+     * as positive sequence positively impact it.
+     */
+    int positiveSeqs = mSeqCounters[LANG_POSITIVE_CAT] * 4;
+    int probableSeqs = mSeqCounters[LANG_PROBABLE_CAT];
+    int neutralSeqs  = mSeqCounters[LANG_NEUTRAL_CAT];
+    int negativeSeqs = mSeqCounters[LANG_NEGATIVE_CAT] * 4;
+    int totalSeqs    = positiveSeqs + probableSeqs + neutralSeqs + negativeSeqs;
+
+    r = ((float)1.0) * (positiveSeqs + probableSeqs - negativeSeqs) / totalSeqs / mModel->mTypicalPositiveRatio;
+    /* The more control characters (proportionnaly to the size of the text), the
+     * less confident we become in the current language.
+     */
+    r = r * (mTotalChar - mCtrlChar) / mTotalChar;
+    r = r * mFreqChar / mTotalChar;
+
+    return r;
+  }
+  return (float)0.01;
+}
+
+const char* nsLanguageDetector::GetLanguage()
+{
+  return mModel->langName;
+}
+
+int nsLanguageDetector::GetOrderFromCodePoint(int codePoint)
+{
+  int max = mModel->charOrderTableSize;
+  int i   = max / 2;
+  int c   = mModel->charOrderTable[i * 2];
+
+  while ((c = mModel->charOrderTable[i * 2]) != codePoint)
+  {
+    if (c > codePoint)
+    {
+      if (i == 0)
+        break;
+      max = i - 1;
+      i = i / 2;
+    }
+    else if (i < max - 1)
+    {
+      i += (max - i) / 2;
+    }
+    else if (i == max - 1)
+    {
+      i = max;
+    }
+    else
+    {
+      break;
+    }
+  }
+
+  return (c == codePoint) ? mModel->charOrderTable[i * 2 + 1] : -1;
+}
diff --git a/src/nsLanguageDetector.h b/src/nsLanguageDetector.h
new file mode 100644
index 0000000..6c22d17
--- /dev/null
+++ b/src/nsLanguageDetector.h
@@ -0,0 +1,119 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is Mozilla Universal charset detector code. This
+ * file was later added by Jehan in 2021 to add language detection.
+ *
+ * The Initial Developer of the Original Code is Netscape Communications
+ * Corporation.
+ * Portions created by the Initial Developer are Copyright (C) 2001 the
+ * Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *          Jehan <zemarmot.net> (2021)
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+#ifndef nsLanguageDetector_h__
+#define nsLanguageDetector_h__
+
+#include "nscore.h"
+
+#define LANG_SB_ENOUGH_REL_THRESHOLD      2048
+#define LANG_POSITIVE_SHORTCUT_THRESHOLD  (float)0.95
+#define LANG_NEGATIVE_SHORTCUT_THRESHOLD  (float)0.05
+
+#define LANG_NUMBER_OF_SEQ_CAT 4
+#define LANG_POSITIVE_CAT      3
+#define LANG_PROBABLE_CAT      2
+#define LANG_NEUTRAL_CAT       1
+#define LANG_NEGATIVE_CAT      0
+
+typedef struct
+{
+  const char*          langName;
+
+  /* Table mapping codepoints to character orders. */
+  const PRUint32*      charOrderTable;
+  int                  charOrderTableSize;
+
+  /* freqCharCount x freqCharCount table of 2-char sequence's frequencies. */
+  const PRUint8* const precedenceMatrix;
+  /* The count of frequent characters.
+   * precedenceMatrix size is the square of this count.
+   * charOrderTable can be bigger as it can contain equivalent
+   * characters. Yet it maps to this range of orders.
+   */
+  int                  freqCharCount;
+
+  float                mTypicalPositiveRatio;
+} LanguageModel;
+
+typedef enum {
+  STATE_DETECTING,
+  STATE_FOUND,
+  STATE_UNLIKELY
+} nsDetectState;
+
+class nsLanguageDetector {
+public:
+  nsLanguageDetector(const LanguageModel *model) : mModel(model) { Reset(); }
+  virtual ~nsLanguageDetector() {}
+
+  /* Unlike nsSingleByteCharSetProber, it is charset-unaware and only
+   * looks at unicode codepoints.
+   */
+  virtual const char*   GetLanguage();
+  virtual nsDetectState HandleData(const int* codepoints, PRUint32 cpLen);
+  virtual void          Reset(void);
+  virtual float         GetConfidence(void);
+
+protected:
+  const LanguageModel* const mModel;
+  nsDetectState              mState;
+  /* Order of last character */
+  int                        mLastOrder;
+
+  PRUint32 mTotalSeqs;
+  PRUint32 mSeqCounters[LANG_NUMBER_OF_SEQ_CAT];
+
+  PRUint32 mTotalChar;
+  PRUint32 mCtrlChar;
+  /* Characters that fall in our sampling range */
+  PRUint32 mFreqChar;
+
+private:
+
+  int GetOrderFromCodePoint(int codePoint);
+};
+
+extern const LanguageModel ArabicModel;
+extern const LanguageModel DanishModel;
+extern const LanguageModel FrenchModel;
+extern const LanguageModel GermanModel;
+extern const LanguageModel ItalianModel;
+extern const LanguageModel SpanishModel;
+
+#endif /* nsLanguageDetector_h__ */