(This is mostly "selfish suggestion" because it is aimed to be usefull for one certain tool. But overall, it seems like good idea for game to be more chatty when anouncing things for people who like to recount history of fort later on for fanfiction stories or who could use some anouncements to be able to react to events that need reaction to. Besides, it does not seem like overly complicated thing to do for most of them.)
Okay, I suggest game log and anouncements to contain theese messages:
* When game is loaded, usefull to know what region/fortress is being logged for consecutive games.
Loaded game for <region name>, fortress <fortress name>. It is <season> of <year>, <month_date> <month>.
* When dwarf is marked as criminal by justice and overall justice messages. Player might want to react to this message.
<dwarf> was found guilty of <crime> and was sentenced for <punishment>.
<dwarf> was imprisoned.
<dwarf> was released from prison.
* Merchants provide unloading goods message, but not "ready to trade" message, which requires close watch on it. Anouncing the fact that player can start trading is usefull.
Merchants have finished unloading and are ready to trade.
* Siege end, purely for historical records.
<race> siege has been broken.
* Animal slaughtering message is a bit confusing because it is same as when animal gets killed by hostiles and knowledge that cat was slaughtered by player isntead of being killed by monster is usefull.
<animal> was slaughtered.
* Hostiles deaths are not logged at all - they should be logged as part of their combat log. Fun for grepping answer for "how many goblins did we kill?"
* Dwarven skill-ups and downs. I have chosen breakpoints after which low-quality products are impossible and first signs of rust so that player can react accrdingly (either ignore or queue some production).
<dwarf> has became Proficient <skill>.
<dwarf> has became Accomplished <skill>.
<dwarf> has became Legendary <skill>.
<dwarf> is now very rusty at <skill>.
<dwarf> forgot great deal of <skill>.
* Animal groups entering/leaving map should be anounced. Important-ish to tip off player that hunters will be doing their thing or that there are new targets for military live practice.
<species> wandered near fortress.
<species> have left.
* Total population after embark wave, for historical records.
There are now <number> <fortress_race> in our fortress.
* Dwarves getting to critical levels of hunger or thirst, somethign that player might want to know in case cosntriction worker walled himself off at inaccessible location.
* Mayor elections, ascendance from expedition-leader led community to mayor-led one. Just to record history better.
* Party ending, as players could want to be tipped off that workforce will be once again avaialble.
* Workshop construction being finished, so that player can immediatelly queue tasks.
<dwarfname> has finished construction of <workshopname>.
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That's it for now.