diff --git a/src/SlashCommands.js b/src/SlashCommands.js
index ae619a1359..185ea504ac 100644
--- a/src/SlashCommands.js
+++ b/src/SlashCommands.js
@@ -186,7 +186,7 @@ const commands = {
                     if (targetRoomId) { break; }
                 }
                 if (!targetRoomId) {
-                    return reject("Unrecognised room alias: " + roomAlias);
+                    return reject(_t("Unrecognised room alias:") +  ' ' + roomAlias);
                 }
             }
         }
@@ -303,14 +303,14 @@ const commands = {
 
                 const device = MatrixClientPeg.get().getStoredDevice(userId, deviceId);
                 if (!device) {
-                    return reject(`Unknown (user, device) pair: (${userId}, ${deviceId})`);
+                    return reject(_t(`Unknown (user, device) pair:`) + ` (${userId}, ${deviceId})`);
                 }
 
                 if (device.isVerified()) {
                     if (device.getFingerprint() === fingerprint) {
-                        return reject(`Device already verified!`);
+                        return reject(_t(`Device already verified!`));
                     } else {
-                        return reject(`WARNING: Device already verified, but keys do NOT MATCH!`);
+                        return reject(_t(`WARNING: Device already verified, but keys do NOT MATCH!`));
                     }
                 }
 
@@ -322,12 +322,15 @@ const commands = {
                     // Tell the user we verified everything!
                     const QuestionDialog = sdk.getComponent("dialogs.QuestionDialog");
                     Modal.createDialog(QuestionDialog, {
-                        title: "Verified key",
+                        title: _t("Verified key"),
                         description: (
                             <div>
                                 <p>
-                                    The signing key you provided matches the signing key you received
-                                    from { userId }'s device { deviceId }. Device marked as verified.
+                                {
+                                    _t("The signing key you provided matches the signing key you received " +
+                                    "from %(userId)s's device %(deviceId)s. Device marked as verified.",
+                                    {userId: userId, deviceId: deviceId})
+                                }
                                 </p>
                             </div>
                         ),
@@ -336,9 +339,13 @@ const commands = {
 
                     return success();
                 } else {
-                    return reject(`WARNING: KEY VERIFICATION FAILED! The signing key for ${userId} and device
-                            ${deviceId} is "${device.getFingerprint()}" which does not match the provided key
-                            "${fingerprint}". This could mean your communications are being intercepted!`);
+                    const fprint = device.getFingerprint();
+                    return reject(
+                        _t('WARNING: KEY VERIFICATION FAILED! The signing key for %(userId)s and device' +
+                           ' %(deviceId)s is "%(fprint)s" which does not match the provided key' +
+                           ' "%(fingerprint)s". This could mean your communications are being intercepted!',
+                            {deviceId: deviceId, fprint: fprint, userId: userId, fingerprint: fingerprint})
+                    );
                 }
             }
         }
@@ -383,7 +390,7 @@ module.exports = {
             if (commands[cmd]) {
                 return commands[cmd].run(roomId, args);
             } else {
-                return reject("Unrecognised command: " + input);
+                return reject(_t("Unrecognised command:") + ' ' + input);
             }
         }
         return null; // not a command
diff --git a/src/components/views/rooms/MessageComposerInput.js b/src/components/views/rooms/MessageComposerInput.js
index a79f71c92d..65148f91ef 100644
--- a/src/components/views/rooms/MessageComposerInput.js
+++ b/src/components/views/rooms/MessageComposerInput.js
@@ -506,7 +506,7 @@ export default class MessageComposerInput extends React.Component {
                     var ErrorDialog = sdk.getComponent("dialogs.ErrorDialog");
                     Modal.createDialog(ErrorDialog, {
                         title: _t("Server error"),
-                        description: ((err && err.message) ? err.message : _t("Server unavailable, overloaded, or something else went wrong") + "."),
+                        description: ((err && err.message) ? err.message : _t("Server unavailable, overloaded, or something else went wrong.")),
                     });
                 });
             }
diff --git a/src/components/views/rooms/MessageComposerInputOld.js b/src/components/views/rooms/MessageComposerInputOld.js
index b664ef4bd3..f6af20c03b 100644
--- a/src/components/views/rooms/MessageComposerInputOld.js
+++ b/src/components/views/rooms/MessageComposerInputOld.js
@@ -316,7 +316,7 @@ export default React.createClass({
                     var ErrorDialog = sdk.getComponent("dialogs.ErrorDialog");
                     Modal.createDialog(ErrorDialog, {
                         title: _t("Server error"),
-                        description: ((err && err.message) ? err.message : _t("Server unavailable, overloaded, or something else went wrong") + "."),
+                        description: ((err && err.message) ? err.message : _t("Server unavailable, overloaded, or something else went wrong.")),
                     });
                 });
             }
diff --git a/src/i18n/strings/en_EN.json b/src/i18n/strings/en_EN.json
index 85e6343359..301e62c2db 100644
--- a/src/i18n/strings/en_EN.json
+++ b/src/i18n/strings/en_EN.json
@@ -215,6 +215,7 @@
   "demote": "demote",
   "Deops user with given id": "Deops user with given id",
   "Default": "Default",
+  "Device already verified!": "Device already verified!",
   "Device ID": "Device ID",
   "Devices": "Devices",
   "Devices will not yet be able to decrypt history from before they joined the room": "Devices will not yet be able to decrypt history from before they joined the room",
@@ -436,7 +437,7 @@
   "Server may be unavailable, overloaded, or search timed out :(": "Server may be unavailable, overloaded, or search timed out :(",
   "Server may be unavailable, overloaded, or the file too big": "Server may be unavailable, overloaded, or the file too big",
   "Server may be unavailable, overloaded, or you hit a bug.": "Server may be unavailable, overloaded, or you hit a bug.",
-  "Server unavailable, overloaded, or something else went wrong": "Server unavailable, overloaded, or something else went wrong",
+  "Server unavailable, overloaded, or something else went wrong.": "Server unavailable, overloaded, or something else went wrong.",
   "Session ID": "Session ID",
   "%(senderName)s set a profile picture.": "%(senderName)s set a profile picture.",
   "%(senderName)s set their display name to %(displayName)s.": "%(senderName)s set their display name to %(displayName)s.",
@@ -460,6 +461,7 @@
   "tag direct chat": "tag direct chat",
   "The default role for new room members is": "The default role for new room members is",
   "The main address for this room is": "The main address for this room is",
+  "The signing key you provided matches the signing key you received from %(userId)s's device %(deviceId)s. Device marked as verified.": "The signing key you provided matches the signing key you received from %(userId)s's device %(deviceId)s. Device marked as verified.",
   "This action cannot be performed by a guest user. Please register to be able to do this": "This action cannot be performed by a guest user. Please register to be able to do this",
   "This email address is already in use": "This email address is already in use",
   "This email address was not found": "This email address was not found",
@@ -521,8 +523,11 @@
   "unknown device": "unknown device",
   "unknown error code": "unknown error code",
   "Unknown room %(roomId)s": "Unknown room %(roomId)s",
+  "Unknown (user, device) pair:": "Unknown (user, device) pair:",
   "unknown": "unknown",
   "Unmute": "Unmute",
+  "Unrecognised command:": "Unrecognised command:",
+  "Unrecognised room alias:": "Unrecognised room alias:",
   "uploaded a file": "uploaded a file",
   "Upload avatar": "Upload avatar",
   "Upload Failed": "Upload Failed",
@@ -538,6 +543,7 @@
   "Verification Pending": "Verification Pending",
   "Verification": "Verification",
   "verified": "verified",
+  "Verified key": "Verified key",
   "Video call": "Video call",
   "Voice call": "Voice call",
   "VoIP conference finished.": "VoIP conference finished.",
@@ -545,6 +551,8 @@
   "VoIP is unsupported": "VoIP is unsupported",
   "(warning: cannot be disabled again!)": "(warning: cannot be disabled again!)",
   "Warning!": "Warning!",
+  "WARNING: Device already verified, but keys do NOT MATCH!": "WARNING: Device already verified, but keys do NOT MATCH!",
+  "WARNING: KEY VERIFICATION FAILED! The signing key for %(userId)s and device %(deviceId)s is \"%(fprint)s\" which does not match the provided key \"%(fingerprint)s\". This could mean your communications are being intercepted!": "WARNING: KEY VERIFICATION FAILED! The signing key for %(userId)s and device %(deviceId)s is \"%(fprint)s\" which does not match the provided key \"%(fingerprint)s\". This could mean your communications are being intercepted!",
   "Who can access this room?": "Who can access this room?",
   "Who can read history?": "Who can read history?",
   "Who would you like to add to this room?": "Who would you like to add to this room?",