--- a/browser/components/preferences/in-content/tests/browser.ini
+++ b/browser/components/preferences/in-content/tests/browser.ini
@@ -44,16 +44,17 @@ skip-if = os != "win" || (os == "win" &&
 [browser_connection.js]
 [browser_connection_bug388287.js]
 [browser_cookies_exceptions.js]
 [browser_defaultbrowser_alwayscheck.js]
 [browser_healthreport.js]
 skip-if = true || !healthreport # Bug 1185403 for the "true"
 [browser_homepages_filter_aboutpreferences.js]
 [browser_extension_controlled.js]
+[browser_languages_subdialog.js]
 [browser_layersacceleration.js]
 [browser_masterpassword.js]
 [browser_notifications_do_not_disturb.js]
 [browser_password_management.js]
 [browser_performance.js]
 skip-if = !e10s
 [browser_performance_e10srollout.js]
 skip-if = !e10s

new file mode 100644
--- /dev/null
+++ b/browser/components/preferences/in-content/tests/browser_languages_subdialog.js
@@ -0,0 +1,62 @@
+add_task(async function() {
+  await openPreferencesViaOpenPreferencesAPI("general", { leaveOpen: true });
+  // eslint-disable-next-line mozilla/no-cpows-in-tests
+  const contentDocument = gBrowser.contentDocument;
+  // eslint-disable-next-line mozilla/no-cpows-in-tests
+  const dialogOverlay = content.gSubDialog._preloadDialog._overlay;
+
+  async function languagesSubdialogOpened() {
+    const promiseSubDialogLoaded = promiseLoadSubDialog("chrome://browser/content/preferences/languages.xul");
+    contentDocument.getElementById("chooseLanguage").click();
+    const win = await promiseSubDialogLoaded;
+    win.Preferences.forceEnableInstantApply();
+    is(dialogOverlay.style.visibility, "visible", "The dialog is visible.");
+    return win;
+  }
+
+  function closeLanguagesSubdialog() {
+    const closeBtn = dialogOverlay.querySelector(".dialogClose");
+    closeBtn.doCommand();
+  }
+
+  is(dialogOverlay.style.visibility, "", "The dialog is invisible.");
+  let win = await languagesSubdialogOpened();
+  ok(win.document.getElementById("spoofEnglish").hidden, "The 'Request English' checkbox is hidden.");
+  closeLanguagesSubdialog();
+  is(dialogOverlay.style.visibility, "", "The dialog is invisible.");
+
+  await SpecialPowers.pushPrefEnv({set: [
+    ["privacy.resistFingerprinting", true],
+    ["privacy.spoof_english", 0],
+  ]});
+
+  win = await languagesSubdialogOpened();
+  ok(!win.document.getElementById("spoofEnglish").hidden, "The 'Request English' checkbox isn't hidden.");
+  ok(!win.document.getElementById("spoofEnglish").checked, "The 'Request English' checkbox isn't checked.");
+  is(win.Preferences.get("privacy.spoof_english").value, 0, "The privacy.spoof_english pref is set to 0.");
+
+  win.document.getElementById("spoofEnglish").checked = true;
+  win.document.getElementById("spoofEnglish").doCommand();
+  ok(win.document.getElementById("spoofEnglish").checked, "The 'Request English' checkbox is checked.");
+  is(win.Preferences.get("privacy.spoof_english").value, 2, "The privacy.spoof_english pref is set to 2.");
+  closeLanguagesSubdialog();
+
+  win = await languagesSubdialogOpened();
+  ok(!win.document.getElementById("spoofEnglish").hidden, "The 'Request English' checkbox isn't hidden.");
+  ok(win.document.getElementById("spoofEnglish").checked, "The 'Request English' checkbox is checked.");
+  is(win.Preferences.get("privacy.spoof_english").value, 2, "The privacy.spoof_english pref is set to 2.");
+
+  win.document.getElementById("spoofEnglish").checked = false;
+  win.document.getElementById("spoofEnglish").doCommand();
+  ok(!win.document.getElementById("spoofEnglish").checked, "The 'Request English' checkbox isn't checked.");
+  is(win.Preferences.get("privacy.spoof_english").value, 1, "The privacy.spoof_english pref is set to 1.");
+  closeLanguagesSubdialog();
+
+  win = await languagesSubdialogOpened();
+  ok(!win.document.getElementById("spoofEnglish").hidden, "The 'Request English' checkbox isn't hidden.");
+  ok(!win.document.getElementById("spoofEnglish").checked, "The 'Request English' checkbox isn't checked.");
+  is(win.Preferences.get("privacy.spoof_english").value, 1, "The privacy.spoof_english pref is set to 1.");
+  closeLanguagesSubdialog();
+
+  gBrowser.removeCurrentTab();
+});

--- a/browser/components/preferences/languages.js
+++ b/browser/components/preferences/languages.js
@@ -314,34 +314,39 @@ var gLanguagesDialog = {
   readSpoofEnglish() {
     var checkbox = document.getElementById("spoofEnglish");
     var resistFingerprinting = Services.prefs.getBoolPref("privacy.resistFingerprinting");
     if (!resistFingerprinting) {
       checkbox.hidden = true;
       return false;
     }
 
-    var spoofEnglish = document.getElementById("privacy.spoof_english").value;
+    var spoofEnglish = Preferences.get("privacy.spoof_english").value;
     var activeLanguages = this._activeLanguages;
     var availableLanguages = this._availableLanguages;
     checkbox.hidden = false;
     switch (spoofEnglish) {
-    case 1: // don't spoof intl.accept_lanauges
+    case 1: // don't spoof intl.accept_languages
       activeLanguages.disabled = false;
       activeLanguages.selectItem(activeLanguages.firstChild);
       availableLanguages.disabled = false;
       this.onAvailableLanguageSelect();
       return false;
-    case 2: // spoof intl.accept_lanauges
+    case 2: // spoof intl.accept_languages
       activeLanguages.clearSelection();
       activeLanguages.disabled = true;
       availableLanguages.disabled = true;
       this.onAvailableLanguageSelect();
       return true;
-    default: // will prompt for spoofing intl.accept_lanauges if resisting fingerprinting
+    default: // will prompt for spoofing intl.accept_languages if resisting fingerprinting
       return false;
     }
   },
 
   writeSpoofEnglish() {
     return document.getElementById("spoofEnglish").checked ? 2 : 1;
   }
 };
+
+// These focus and resize handlers hack around XUL bug 1194844
+// by triggering extra reflow (see bug 1194346).
+window.addEventListener("focus", () => gLanguagesDialog.forceReflow());
+window.addEventListener("resize", () => gLanguagesDialog.forceReflow());

--- a/browser/components/preferences/languages.xul
+++ b/browser/components/preferences/languages.xul
@@ -21,22 +21,17 @@
         buttons="accept,cancel,help"
         persist="lastSelected screenX screenY"
         closebuttonlabel="&preferencesCloseButton.label;"
         closebuttonaccesskey="&preferencesCloseButton.accesskey;"
         role="dialog"
         onload="gLanguagesDialog.init();"
         helpTopic="prefs-languages"
         ondialoghelp="openPrefsHelp()"
-        style="width: &window.width;"
-        onfocus="gLanguagesDialog.forceReflow()"
-        onresize="gLanguagesDialog.forceReflow()">
-
-<!-- The onfocus and onresize handlers above hack around XUL bug 1194844
-   - by triggering extra reflow (see bug 1194346). -->
+        style="width: &window.width;">
 
   <script type="application/javascript" src="chrome://browser/content/utilityOverlay.js"/>
   <script type="application/javascript" src="chrome://global/content/preferencesBindings.js"/>
   <script type="application/javascript" src="chrome://browser/content/preferences/languages.js"/>
 
   <keyset>
     <key key="&windowClose.key;" modifiers="accel" oncommand="Preferences.close(event)"/>
   </keyset>