In Arabic generally, especially in Egyptian or Gulf Arabic, they say أحداث ١١ سبتمبر ahdath hadi ‘ashar sibtambir, which literally means ‘the events of September 11’. In Levantine or Iraqi Arabic they may alternatively say أحداث ١١ أيلول ahdath hadi ‘ashar aylul, using the name for September current in those countries.
It grates on me to hear Americans referring to September 11 as “nine one one.” I recently heard someone on a radio talk show say that. Please knock it off!
hardly a joke:
As an aside, when car companies started installing emergency releases in trunks so that kids wouldn’t be trapped, the engineers wanted to use a glowing red handle. Child pychologists advised against it. Kids are taught not to touch such dangerous things. The handles are green.
Like severus said, in French-speaking Canada it’s mostly “les attentats du onze septembre” (attacks). Also used is “les événements du onze septembre” (events), or simply “le onze septembre”. When used by itself, it is common to hyphenate — “11-septembre” —, for example in the expression “nous devons tout faire pour empêcher un autre 11-septembre”, “we must do everything we can to prevent another September 11”.
I might add that Ground Zero is not translated.
i.e. Literal: the attacks on September 11th. 
(Autumn-month? You don’t translate januari as “Roman-two-faced-god-month”…) “Isku” translates as “blow”, “strike”, or “hit”.
“Syyskuun 11. päivä” (“September 11th”, literally “the 11th day of September”) or “11. syyskuuta” is the standard way of referring to the attacks, since now everyone associates this date with those specific events. However, it’s basically just how we say a date, except usually we leave the “päivä” out of it; yesterday was “26. elokuuta” or “elokuun 26. päivä” (or “elokuun kahdeskymmeneskuudes” for short ;)).
We don’t really use the “9/11” term because we write dates dd/mm/yy, but I’ve seen it used on message boards and such occasionally.
Exactly parallel in Mexico, in my experience. Usually called “el once de septiembre” (i.e., September 11), but occasionally something like “lo de las torres gemelas” (roughly, “That Twin Towers thing”).
When watching the French news story about last month’s steampipe explosion in NYC, I heard “onze de septembre” and figured they were relating it somehow to September 11th.
Incidentally, when I googled “onze de setembre” (Catalan for “September 11”), the first ten references were to the Catalan national day, commemorating a defeat in 1714, plus one reference to the coup in Chile in 1973. The Catalan Wikipedia article is entitled “Atacs terroristes de l’11 de setembre de 2001” (terrorist attacks of 11 September 2001).
Apropos of nothing, it irritated me greatly last year to hear the newsbeings saying “it’s the fifth anniversary of September 11.” No, it is September 11.