how do we say today's date in english ? is there any differnce regenal differnces
i sometimes hear" it is September nine, 2011".. is it correct or that is just informal

Question

Answer

There are no real regional differences.  
Normally you say the Month, day, and year.  Often we use ordinal numbers.  That is, numbers with have the suffix -st, -nd, -rd, -th.  This makes no difference.

So you could read the date today as 
November one, two thousand eleven.
or 
November first, two thousand eleven.

Answer

September 9th, 2011.

Month, day, year.

Answer

If by 'regionally', you mean 'globally', then British English is different to US English. In spoken UK English it is any of the following: 

"The ninth of September, two thousand and eleven" 
"The ninth of September, twenty-eleven" 
"September the ninth, two thousand and eleven" 
"September the ninth, twenty-eleven" 

Having said that, the US formats are heard much more often now, especially on the radio,

Answer

There are differences of style but not really of region.

November 1, 2011. (standard American way of writing the date: month-day-year)
11/1/2011
11/1/11

2011-11-01    (current military style: year-month-day)
20111101       also military (marines)

1Nov11 or 1 Nov 11       (old military style [Korean War] day-month-year)

November first.
November 1st.
The first of November

I would say that September nine, 2011 is neither correct nor common, although it does get the idea across.

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