Do people outside of the USA use two-part date abbreviations for the current year? For instance, representing the last day of May, you might see someone enter 5/31 into a date field.
Do international users do something similar? In a country that ordinarily uses dd/MM/yyyy would they use 31/5 or some such?
Yes, there are different ways of entering a data in a short format. The CLDR chart on Md notations illustrates the variation. Many languages use d/M notation, but d.M, M-d, and other notations are used, too. The notations used in CLDR are explained in the LDML specification; “Md” stands for month and date notation consisting of shortest possible numeric notation for month, M, and day, d, with language-dependent punctuation and order.
The M/d vs. d/M case is particularly problematic, because both notations are used in English, as well as in other languages.
Data consisting of two numbers separated by a slash should be accepted on input only if you can be sure to know which of the two different notations M/d and d/M is meant. When can you be sure of such things? Just giving people instructions doesn’t guarantee anything. Calendar widgets for input have their problems, but at least they avoid the confusion between 4/7 and 7/4.
There is a good map here http://en.wikipedia.org/wiki/Date_format_by_country that shows only really the States uses (and Belize!) Middle-Endian MM/DD/YYYY date format, most use Little-Endian DD/MM/YYYY and some use Big Endian (mostly Asian) YYYY-MM-DD. Philipines uses both Little and Middle due to American influence, as does Saudi Arabia - must get very confusing there!
The simple answer is yes. It is extremely annoying trying to sort information with a mix of dates formats
Consider using ISO 8601 date formats when printing dates and times. When inputting free form dates clearly indicate the convention you are expecting. Depending on convention 1/12/2012 could be early or late in the year.
From my experience, I can testify that this is common practice at least in Germany (31. 5. or 31. 05.) and the Netherlands (31-5, 31-05). Additionally, both countries regularly use 05/12 (sometimes 05/'12) to mean "May 2012".
In my country, we use d M. In speech, nobody ever says 10 May; we say 10th of May. For the sake of being clear, I always state the required format in my application, or supplier calendar picker. Also, for the sake of my programmers & clients, who may set their computer regional settings to whatever they please, I always program dates as string.
See more about this in this post of mine: Is Date a String or a complex object?
Since you are in software engineering: Read the documentation of your operating system to find out how to display a date correctly for any language / region combination that the user choses, and how to parse date input accordingly.
You will encounter any possible combination. You'll have rules about abbreviating the year or not, how to separate the different components and so on. If you spell month names, they have different names in different countries, different and sometimes inconsistent ways to abbreviate them.
