１月、2月…をJan. Feb. ...に変換する

可読性のよいやり方↓

        public static string GetMonthStringEn(int month)
        {
            var date = new DateTime(2000, month, 1);
            System.Globalization.CultureInfo ci = new System.Globalization.CultureInfo("en-US");

            return date.ToString("MMM", ci) + ".";
        }

別解↓

        public static string GetMonthStringEn(int month)
        {
            var invariantCulture = new CultureInfo(string.Empty, false);
            var monthString = DateTimeFormatInfo.GetInstance(invariantCulture).AbbreviatedMonthNames[month - 1];

            return monthString + ".";
        }