XAFORUM-48: Warnings when deleting a Topic

This macro seems to be generic, so why does the key (used for generic 'no mail sent' errors) contain a specific action ('deleteconversation') in its name?

You should remove that part from the key or replace it with something more generic like 'action' or whatever fits best.

General note about translation key naming:
You need to be aware that all the translation keys from both XWiki itself and any installed application are currently put in the same scope/place/bucket. This means that if you do not use an unique name for your translation key, you risk overriding another application's translation (or the other way around). To avoid this, we currently recommend prefixing all the application's translation keys with the application name. In the forum application's example, the translation key prefix should be "forum." to avoid conflicts.