diff --git a/autotests/test_highlighter.cpp b/autotests/test_highlighter.cpp
--- a/autotests/test_highlighter.cpp
+++ b/autotests/test_highlighter.cpp
@@ -24,6 +24,7 @@
     void testEnglish();
     void testFrench();
     void testMultipleLanguages();
+    void testForceLanguage();
 };
 
 void HighlighterTest::initTestCase()
@@ -95,6 +96,30 @@
     QVERIFY2(suggestionsForDict.contains(QLatin1String("dictionnaire")), qPrintable(suggestionsForDict.join(QLatin1Char(','))));
 }
 
+void HighlighterTest::testForceLanguage()
+{
+    // GIVEN
+    QPlainTextEdit textEdit;
+    textEdit.setPlainText(QString::fromLatin1(s_frenchSentence));
+    Sonnet::Highlighter highlighter(&textEdit);
+    highlighter.setCurrentLanguage(QStringLiteral("en"));
+    QVERIFY(highlighter.spellCheckerFound());
+    QVERIFY(highlighter.autoDetectLanguageDisabled());
+    highlighter.rehighlight();
+    QCOMPARE(highlighter.currentLanguage(), QStringLiteral("en"));
+    QTextCursor cursor(textEdit.document());
+
+    // WHEN
+    cursor.setPosition(0);
+    const QStringList suggestionsForBnjour = highlighter.suggestionsForWord(QStringLiteral("Bnjour"), cursor);
+    cursor.setPosition(37);
+    const QStringList suggestionsForDict = highlighter.suggestionsForWord(QStringLiteral("dictionnare"), cursor);
+
+    // THEN
+    QVERIFY2(!suggestionsForBnjour.contains(QLatin1String("Bonjour")), qPrintable(suggestionsForBnjour.join(QLatin1Char(','))));
+    QVERIFY2(!suggestionsForDict.contains(QLatin1String("dictionnaire")), qPrintable(suggestionsForDict.join(QLatin1Char(','))));
+}
+
 void HighlighterTest::testMultipleLanguages()
 {
     // GIVEN
diff --git a/src/core/backgroundchecker.h b/src/core/backgroundchecker.h
--- a/src/core/backgroundchecker.h
+++ b/src/core/backgroundchecker.h
@@ -72,6 +72,25 @@
      */
     bool addWordToSession(const QString &word);
 
+    /**
+     * Returns whether the automatic language detection is disabled,
+     * overriding the Sonnet settings.
+     *
+     * @return true if the automatic language detection is disabled
+     * @since 5.71
+     */
+    bool autoDetectLanguageDisabled() const;
+
+    /**
+     * Sets whether to disable the automatic language detection.
+     *
+     * @param autoDetectDisabled if true, the language will not be
+     * detected automatically by the spell checker, even if the option
+     * is enabled in the Sonnet settings.
+     * @since 5.71
+     */
+    void setAutoDetectLanguageDisabled(bool autoDetectDisabled);
+
 public Q_SLOTS:
     virtual void start();
     virtual void stop();
diff --git a/src/core/backgroundchecker.cpp b/src/core/backgroundchecker.cpp
--- a/src/core/backgroundchecker.cpp
+++ b/src/core/backgroundchecker.cpp
@@ -48,7 +48,7 @@
         const bool ignoreUpperCase = !currentDict.testAttribute(Speller::CheckUppercase);
         while (mainTokenizer.hasNext()) {
             QStringRef sentence = mainTokenizer.next();
-            if (autodetectLanguage) {
+            if (autodetectLanguage && !autoDetectLanguageDisabled) {
                 if (!mainTokenizer.isSpellcheckable()) {
                     continue;
                 }
@@ -119,8 +119,19 @@
 {
 }
 
+bool BackgroundChecker::autoDetectLanguageDisabled() const
+{
+    return d->autoDetectLanguageDisabled;
+}
+
+void BackgroundChecker::setAutoDetectLanguageDisabled(bool autoDetectDisabled)
+{
+    d->autoDetectLanguageDisabled = autoDetectDisabled;
+}
+
 void BackgroundChecker::setSpeller(const Speller &speller)
 {
+    d->autoDetectLanguageDisabled = true;
     d->currentDict = speller;
 }
 
@@ -152,6 +163,7 @@
 void BackgroundChecker::changeLanguage(const QString &lang)
 {
     // this sets language only for current sentence
+    d->autoDetectLanguageDisabled = true;
     d->currentDict.setLanguage(lang);
 }
 
diff --git a/src/core/backgroundchecker_p.h b/src/core/backgroundchecker_p.h
--- a/src/core/backgroundchecker_p.h
+++ b/src/core/backgroundchecker_p.h
@@ -23,6 +23,7 @@
     BackgroundCheckerPrivate() : mainTokenizer(new SentenceTokenizer)
         , sentenceOffset(-1)
     {
+        autoDetectLanguageDisabled = false;
     }
 
     void start();
@@ -33,6 +34,7 @@
     QStringRef lastMisspelled;
     Speller currentDict;
     int sentenceOffset;
+    bool autoDetectLanguageDisabled;
 
 private Q_SLOTS:
     void checkNext();
diff --git a/src/ui/highlighter.h b/src/ui/highlighter.h
--- a/src/ui/highlighter.h
+++ b/src/ui/highlighter.h
@@ -90,6 +90,25 @@
      */
     void setAutomatic(bool automatic);
 
+    /**
+     * Returns whether the automatic language detection is disabled,
+     * overriding the Sonnet settings.
+     *
+     * @return true if the automatic language detection is disabled
+     * @since 5.71
+     */
+    bool autoDetectLanguageDisabled() const;
+
+    /**
+     * Sets whether to disable the automatic language detection.
+     *
+     * @param autoDetectDisabled if true, the language will not be
+     * detected automatically by the spell checker, even if the option
+     * is enabled in the Sonnet settings.
+     * @since 5.71
+     */
+    void setAutoDetectLanguageDisabled(bool autoDetectDisabled);
+
     /**
      * Adds the given word permanently to the dictionary. It will never
      * be marked as misspelled again, even after restarting the application.
diff --git a/src/ui/highlighter.cpp b/src/ui/highlighter.cpp
--- a/src/ui/highlighter.cpp
+++ b/src/ui/highlighter.cpp
@@ -79,6 +79,7 @@
         tokenizer = new WordTokenizer();
         active = true;
         automatic = false;
+        autoDetectLanguageDisabled = false;
         connected = false;
         wordCount = 0;
         errorCount = 0;
@@ -118,6 +119,7 @@
     QPlainTextEdit *plainTextEdit = nullptr;
     bool active;
     bool automatic;
+    bool autoDetectLanguageDisabled;
     bool completeRehighlightRequired;
     bool intraWordEditing;
     bool spellCheckerFound; //cached d->dict->isValid() value
@@ -195,6 +197,11 @@
     return d->automatic;
 }
 
+bool Highlighter::autoDetectLanguageDisabled() const
+{
+    return d->autoDetectLanguageDisabled;
+}
+
 bool Highlighter::intraWordEditing() const
 {
     return d->intraWordEditing;
@@ -217,6 +224,11 @@
     }
 }
 
+void Highlighter::setAutoDetectLanguageDisabled(bool autoDetectDisabled)
+{
+    d->autoDetectLanguageDisabled = autoDetectDisabled;
+}
+
 void Highlighter::slotAutoDetection()
 {
     bool savedActive = d->active;
@@ -326,7 +338,7 @@
         const bool autodetectLanguage = d->spellchecker->testAttribute(Speller::AutoDetectLanguage);
         while (d->languageFilter->hasNext()) {
             QStringRef sentence = d->languageFilter->next();
-            if (autodetectLanguage) {
+            if (autodetectLanguage && !d->autoDetectLanguageDisabled) {
                 QString lang;
                 QPair<int, int> spos = QPair<int, int>(sentence.position(), sentence.length());
                 // try cache first
@@ -383,6 +395,7 @@
         d->spellchecker->setLanguage(prevLang);
         return;
     }
+    d->autoDetectLanguageDisabled = true;
     d->wordCount = 0;
     d->errorCount = 0;
     if (d->automatic || d->active) {