Well, generally it's when they kill someone (a sapient someone), isn't it ?
That's a fairly easy one to pull off, but there is also being a child of a historical figure, being some sort of explorer or adventurer, being a leader of any kind, or making some sort of notable object whether it is an artifact or just some masterwork crafts and becoming a legendary crafter.
About language, I think that it will part of a "Culture" arc, because there are a LOT of things to do (and very interesting one) to differenciate cultures. Look at what Ultima Ratio Regum has tried to do on this part.
But about dialogue and conversation I wondered something.
Some RPG have very advanced (of course, scripted) talks between you and your PNJ companions (such as, for example most Obsidian games), while others have very minimal or no "psychological" interaction. How do you envision interaction between you and your companion(s) ? Are you happy with the current state of this part of the game, do you plan in a middle/long term to change it, and if yes, how (=to what) ?
Toady wants to allow marriage and romance at some point, and if you can have romance with anyone, why not your followers?
In any event, as long as there's a Language Arc in the future, I can't imagine there isn't further rewrites of dialogue that will go with it.
About the language arc, I wonder if toady is still planning to procedurally generate actual text snippets/paragraphs in books for players to translate or if he has completely decided that that probably isn't "doable", it wouldn't surprise me if he still wanted to accomplish it, he isn't one to shy away from something so challenging.
Theoretically not necessarily impossible, but it would be fiddly. Off the top of my head you'd divide general statements into categories - questions, answers, greetings, etc. I suppose you'd have to get the program to recognise each separate part of a sentence, like 'Hi, how are you?' and then structure something around that. So:
'Hi' is the greeting - it's interchangeable with a number of other single word greeting, or possibly some more elaborate ones.
Then you've got the question type - in this case you can conceivably swap 'how' out with 'why', 'where', 'what', etc. Then 'are' could be one of a similar list, - 'were', 'do', 'can', etc. and then the subject - 'you', 'he', 'she', 'it', 'they', '[name]' etc.
Of course, that has the ability to generate some... interesting questions, and it's pretty simplistic. But it does get quite stodgy when you start going into all the sub-categories any one word can occupy depending on context.