Silence's WML Questions

[Elvish_Hunter]

Neither message was shown: from that, I assume that something is wrong with name="turn $($turn_number| + 4)" but I don't know what it is.

There's something fishy going on here...
Seriously, when you have an event name like this, each turn the game will look for a turn number greater by 4 than the current one. Needless to say, it will never work - not correctly, at least.
You have two solutions:
1) keep this syntax and try adding delayed_variable_substitution=no. This will acquire the turn number from the parent event, so sooner or later $turn_number+4 will mean something useful.
2) use variables. When the parent event is fired, you set a variable containing the turn number. Then you add 4 to that variable. Then you use an [event] with [filter_condition] to check if the variable turn number equals to your variable. It will be longer to write, but simpler to understand. Your call.