Make slash command errors translatable but also work in rageshakes (#7377)

See https://github.com/matrix-org/matrix-react-sdk/pull/7372#discussion_r769556546

We want the error to be translated for the user but not in our rageshake logs.

Also updates some error messages to give more info.

src/components/views/rooms/SendMessageComposer.tsx

@@ -378,6 +378,9 @@ export class SendMessageComposer extends React.Component<ISendMessageComposerPro
             let errText;
             if (typeof error === 'string') {
                 errText = error;
+            } else if (error.translatedMessage) {
+                // Check for translatable errors (newTranslatableError)
+                errText = error.translatedMessage;
             } else if (error.message) {
                 errText = error.message;
             } else {