--- a/toolkit/content/aboutSupport.js
+++ b/toolkit/content/aboutSupport.js
@@ -802,16 +802,34 @@ var snapshotFormatters = {
         ];
         for (let arg of syscall.args) {
           cells.push($.new("td", arg, "integer"));
         }
         syscallBody.appendChild($.new("tr", cells));
       }
     }
   },
+
+  intl: function intl(data) {
+    $("intl-locale-requested").textContent =
+      JSON.stringify(data.localeService.requested);
+    $("intl-locale-available").textContent =
+      JSON.stringify(data.localeService.available);
+    $("intl-locale-supported").textContent =
+      JSON.stringify(data.localeService.supported);
+    $("intl-locale-regionalprefs").textContent =
+      JSON.stringify(data.localeService.regionalPrefs);
+    $("intl-locale-default").textContent =
+      JSON.stringify(data.localeService.defaultLocale);
+
+    $("intl-osprefs-systemlocales").textContent =
+      JSON.stringify(data.osPrefs.systemLocales);
+    $("intl-osprefs-regionalprefs").textContent =
+      JSON.stringify(data.osPrefs.regionalPrefsLocales);
+  }
 };
 
 var $ = document.getElementById.bind(document);
 
 $.new = function $_new(tag, textContentOrChildren, className, attributes) {
   let elt = document.createElement(tag);
   if (className)
     elt.className = className;

--- a/toolkit/content/aboutSupport.xhtml
+++ b/toolkit/content/aboutSupport.xhtml
@@ -746,13 +746,84 @@
 	    </tr>
 	</thead>
 	<tbody id="sandbox-syscalls-tbody">
 	</tbody>
       </table>
 #endif
 #endif
 
+      <h2 class="major-section">
+        &aboutSupport.intlTitle;
+      </h2>
+
+      <table>
+        <tbody id="intl-localeservice-tbody">
+          <tr>
+            <th colspan="2" class="title-column">
+              &aboutSupport.intlAppTitle;
+            </th>
+          </tr>
+          <tr>
+            <th class="column">
+              &aboutSupport.intlLocalesRequested;
+            </th>
+            <td id="intl-locale-requested">
+            </td>
+          </tr>
+          <tr>
+            <th class="column">
+              &aboutSupport.intlLocalesAvailable;
+            </th>
+            <td id="intl-locale-available">
+            </td>
+          </tr>
+          <tr>
+            <th class="column">
+              &aboutSupport.intlLocalesSupported;
+            </th>
+            <td id="intl-locale-supported">
+            </td>
+          </tr>
+          <tr>
+            <th class="column">
+              &aboutSupport.intlRegionalPrefs;
+            </th>
+            <td id="intl-locale-regionalprefs">
+            </td>
+          </tr>
+          <tr>
+            <th class="column">
+              &aboutSupport.intlLocalesDefault;
+            </th>
+            <td id="intl-locale-default">
+            </td>
+          </tr>
+        </tbody>
+        <tbody id="intl-ospreferences-tbody">
+          <tr>
+            <th colspan="2" class="title-column">
+              &aboutSupport.intlOSTitle;
+            </th>
+          </tr>
+          <tr>
+            <th class="column">
+              &aboutSupport.intlOSPrefsSystemLocales;
+            </th>
+            <td id="intl-osprefs-systemlocales">
+            </td>
+          </tr>
+          <tr>
+            <th class="column">
+              &aboutSupport.intlRegionalPrefs;
+            </th>
+            <td id="intl-osprefs-regionalprefs">
+            </td>
+          </tr>
+        </tbody>
+      </table>
+      <!-- - - - - - - - - - - - - - - - - - - - - -->
+
     </div>
 
   </body>
 
 </html>

--- a/toolkit/locales/en-US/chrome/global/aboutSupport.dtd
+++ b/toolkit/locales/en-US/chrome/global/aboutSupport.dtd
@@ -150,8 +150,18 @@ variant of aboutSupport.showDir.label. -
 <!ENTITY aboutSupport.mediaDeviceGroup "Group">
 <!ENTITY aboutSupport.mediaDeviceVendor "Vendor">
 <!ENTITY aboutSupport.mediaDeviceState "State">
 <!ENTITY aboutSupport.mediaDevicePreferred "Preferred">
 <!ENTITY aboutSupport.mediaDeviceFormat "Format">
 <!ENTITY aboutSupport.mediaDeviceChannels "Channels">
 <!ENTITY aboutSupport.mediaDeviceRate "Rate">
 <!ENTITY aboutSupport.mediaDeviceLatency "Latency">
+
+<!ENTITY aboutSupport.intlTitle "Internationalization &amp; Localization">
+<!ENTITY aboutSupport.intlAppTitle "Application Settings">
+<!ENTITY aboutSupport.intlLocalesRequested "Requested Locales">
+<!ENTITY aboutSupport.intlLocalesAvailable "Available Locales">
+<!ENTITY aboutSupport.intlLocalesSupported "App Locales">
+<!ENTITY aboutSupport.intlLocalesDefault "Default Locale">
+<!ENTITY aboutSupport.intlOSTitle "Operating System">
+<!ENTITY aboutSupport.intlOSPrefsSystemLocales "System Locales">
+<!ENTITY aboutSupport.intlRegionalPrefs "Regional Preferences">

--- a/toolkit/modules/Troubleshoot.jsm
+++ b/toolkit/modules/Troubleshoot.jsm
@@ -646,17 +646,35 @@ var dataProviders = {
   },
 
   userJS: function userJS(done) {
     let userJSFile = Services.dirsvc.get("PrefD", Ci.nsIFile);
     userJSFile.append("user.js");
     done({
       exists: userJSFile.exists() && userJSFile.fileSize > 0,
     });
-  }
+  },
+
+  intl: function intl(done) {
+    const osPrefs =
+      Cc["@mozilla.org/intl/ospreferences;1"].getService(Ci.mozIOSPreferences);
+    done({
+      localeService: {
+        requested: Services.locale.getRequestedLocales(),
+        available: Services.locale.getAvailableLocales(),
+        supported: Services.locale.getAppLocalesAsBCP47(),
+        regionalPrefs: Services.locale.getRegionalPrefsLocales(),
+        defaultLocale: Services.locale.defaultLocale,
+      },
+      osPrefs: {
+        systemLocales: osPrefs.getSystemLocales(),
+        regionalPrefsLocales: osPrefs.getRegionalPrefsLocales()
+      },
+    });
+  },
 };
 
 if (AppConstants.MOZ_CRASHREPORTER) {
   dataProviders.crashes = function crashes(done) {
     let CrashReports = Cu.import("resource://gre/modules/CrashReports.jsm").CrashReports;
     let reports = CrashReports.getReports();
     let now = new Date();
     let reportsNew = reports.filter(report => (now - report.date < Troubleshoot.kMaxCrashAge));

--- a/toolkit/modules/tests/browser/browser_Troubleshoot.js
+++ b/toolkit/modules/tests/browser/browser_Troubleshoot.js
@@ -739,16 +739,62 @@ const SNAPSHOT_SCHEMA = {
                   type: "string",
                 },
               },
             },
           },
         },
       },
     },
+    intl: {
+      required: true,
+      type: "object",
+      properties: {
+        localeService: {
+          required: true,
+          type: "object",
+          properties: {
+            requested: {
+              required: true,
+              type: "array"
+            },
+            available: {
+              required: true,
+              type: "array"
+            },
+            supported: {
+              required: true,
+              type: "array"
+            },
+            regionalPrefs: {
+              required: true,
+              type: "array"
+            },
+            defaultLocale: {
+              required: true,
+              type: "string"
+            },
+          },
+        },
+        osPrefs: {
+          required: true,
+          type: "object",
+          properties: {
+            systemLocales: {
+              required: true,
+              type: "array"
+            },
+            regionalPrefsLocales: {
+              required: true,
+              type: "array"
+            },
+          },
+        },
+      },
+    },
   },
 };
 
 /**
  * Throws an Error if obj doesn't conform to schema.  That way you get a nice
  * error message and a stack to help you figure out what went wrong, which you
  * wouldn't get if this just returned true or false instead.  There's still
  * room for improvement in communicating validation failures, however.