diff --git a/mozilla/extensions/irc/locales/en-US/chrome/chatzilla.properties b/mozilla/extensions/irc/locales/en-US/chrome/chatzilla.properties
index 1cfb9f8360b..1f4bb33d94d 100644
--- a/mozilla/extensions/irc/locales/en-US/chrome/chatzilla.properties
+++ b/mozilla/extensions/irc/locales/en-US/chrome/chatzilla.properties
@@ -741,7 +741,6 @@ cmd.whowas.help   = Displays the last known information about the user <nickname
 ## dispatch-related error messages ##
 msg.err.internal.dispatch = Internal error dispatching command ``%1$S''.
 msg.err.internal.hook   = Internal error processing hook ``%1$S''.
-msg.err.no.command      = No command named ``%1$S''.
 msg.err.invalid.param   = Invalid value for parameter %1$S (%2$S).
 msg.err.disabled        = Sorry, ``%1$S'' is currently disabled.
 msg.err.notimplemented  = Sorry, ``%1$S'' has not been implemented.
@@ -762,13 +761,13 @@ msg.err.pluginapi.noenable  = Plugin <%1$S> does not have an enable() method.
 msg.err.pluginapi.nodisable = Plugin <%1$S> does not have a disable() method.
 msg.err.invalid.scheme  = Invalid scheme in url <%1$S>.
 msg.err.item.not.found  = Startup script item <%1$S> does not exist or is inaccessible.
-msg.err.unknown.pref    = Unknown pref name ``%1$S''.
-msg.err.unknown.network = Unknown network ``%S''.
-msg.err.unknown.channel = Unknown channel ``%S''.
-msg.err.unknown.user    = Unknown user ``%S''.
-msg.err.unknown.command = Unknown command ``%S''.
+msg.err.unknown.pref    = The preference ``%1$S'' is not known to ChatZilla.
+msg.err.unknown.network = The network ``%S'' is not known to ChatZilla.
+msg.err.unknown.channel = The channel ``%S'' is not known to ChatZilla.
+msg.err.unknown.user    = The user ``%S'' is not known to ChatZilla.
+msg.err.unknown.command = The command ``%S'' is not known to ChatZilla.
 msg.err.unknown.stalk   = Not stalking %S.
-msg.err.unknown.motif   = Unknown motif ``%S''.
+msg.err.unknown.motif   = The motif ``%S'' is not known to ChatZilla.
 msg.err.invalid.charset = Invalid character encoding mode ``%S''.
 msg.err.improper.view   = ``%S'' cannot be used from this view.
 msg.err.not.connected   = Not connected.
@@ -814,6 +813,7 @@ msg.irc.381 = You are now an IRC Operator.
 msg.irc.401 = The nickname ``%S'' does not exist.
 msg.irc.402 = The server ``%S'' does not exist.
 msg.irc.403 = The channel ``%S'' does not exist.
+msg.irc.421 = The command ``%S'' is not known to the server.
 msg.irc.464 = Incorrect password, please try again with the correct password.
 msg.irc.464.login = Please specify your password using the "/pass" command to continue connecting.
 msg.irc.471 = This channel has reached its set capacity; you cannot join it.
@@ -829,8 +829,6 @@ msg.irc.471.knock = %S You might be able to use "/knock %S" to ask the channel o
 msg.irc.473.knock = %S Use "/knock %S" to ask the channel operators to invite you in. [[Knock][Asks the channel operators to let you in][%S]]
 msg.irc.475.knock = %S You might be able to use "/knock %S" to ask the channel operators to invite you in. [[Knock][Asks the channel operators to let you in][%S]]
 
-msg.warn.unk.command    = Unknown command ``%S'', just guessing.
-
 msg.val.on  = on
 msg.val.off = off
 
diff --git a/mozilla/extensions/irc/xul/content/commands.js b/mozilla/extensions/irc/xul/content/commands.js
index 1ca704829c6..195abc92faa 100644
--- a/mozilla/extensions/irc/xul/content/commands.js
+++ b/mozilla/extensions/irc/xul/content/commands.js
@@ -373,7 +373,7 @@ function dispatch(text, e, isInteractive, flags)
     var ary = text.match(/(\S+) ?(.*)/);
     if (!ary)
     {
-        display(getMsg(MSG_ERR_NO_COMMAND, ""));
+        display(getMsg(MSG_ERR_UNKNOWN_COMMAND, ""));
         return null;
     }
 
@@ -399,7 +399,7 @@ function dispatch(text, e, isInteractive, flags)
                 return dispatch("quote", e2);
             }
 
-            display(getMsg(MSG_NO_CMDMATCH, e.commandText), MT_ERROR);
+            display(getMsg(MSG_ERR_UNKNOWN_COMMAND, e.commandText), MT_ERROR);
             break;
 
         case 1:
@@ -1371,7 +1371,7 @@ function cmdHelp(e)
 
     if (ary.length == 0)
     {
-        display(getMsg(MSG_ERR_NO_COMMAND, e.pattern), MT_ERROR);
+        display(getMsg(MSG_ERR_UNKNOWN_COMMAND, e.pattern), MT_ERROR);
         return;
     }
 
diff --git a/mozilla/extensions/irc/xul/content/handlers.js b/mozilla/extensions/irc/xul/content/handlers.js
index 0975ad1e8da..1c35919ca82 100644
--- a/mozilla/extensions/irc/xul/content/handlers.js
+++ b/mozilla/extensions/irc/xul/content/handlers.js
@@ -2292,7 +2292,7 @@ function my_netwallops(e)
 CIRCNetwork.prototype.on421 =
 function my_421(e)
 {
-    this.display(getMsg(MSG_ERR_UNKNOWN_COMMAND, e.params[2]), MT_ERROR);
+    this.display(getMsg(MSG_IRC_421, e.decodeParam(2)), MT_ERROR);
     return true;
 }