Practically every country for business purposes.
No. Some countries use different calendars. So for example you have a Hebrew calendar, a Chinese calendar, an Islamic calendar, a Hindu calendar and many others. For those that use the Gregorian calendar, the months are the same around the world.
Not a country, but Foula still uses the Julian calendar
A Julian year is the same as a calendar year. We use a Gregorian calendar instead of a Julian calendar and have 3 fewer leap years every 400 years. Some Orthodox Churches follow a Julian calendar. They celebrate Christmas later than other Christians.
No. Much of the world uses the Julian calendar, which includes an extra day in Leap Year, and the Hebrew calendar includes a leap MONTH every few years, but the Islamic calendar does not. However, even in the parts of the world that use traditional non-Julian calendars, the standard western calendar is understood and used for the purposes of most international commerce and communications needs.
A calendar
No. There is the Gregorian calendar (used by Americans, Europeans, and Japanese), a Hebrew calendar, and a Muslim calendar at least. Here's a link to a Chinese calendar and an Indian calendar.
The Gregorian calendar is the calendar we use today. So, yes, it does have 12 months.
The ISO calendar is primarily a fiscal calendar and does not change the names of the days of the week, although it does number them differently, starting with 1 on Monday and ending with 7 on Sunday, however Monday on the ISO calendar is also the same Monday on the Gregorian calendar (day 2) and the same Monday that is on the Jewish calendar. Shabbot (or Saturday) does not change. It is still on the same day. But all that is really not relevant, as the keeping of Shabbot is based on the command in the Torah which is based on the Hebrew calendar. So it would not matter what calendar was in use by any country, even if it did mess with the definition of the week, the Hebrew calendar remains the same.
Judaism uses lunar and solar together. They add an occasional leap-month to reconcile it to the solar calendar. Islam uses the lunar calendar exclusively. Druids use the Lunar calendar; and Christians use the Lunar calendar to calculate Easter every year. Some Satanists and Pagans use the Lunar Calendar. In fact the Lunar calendar is used by everyone to some degree.
Most countries use the Gregorian calendar, as the U.S. does. However some cultures use calendars that apply the same rules as the Gregorian calendar does. One example would be the Chinese Leap year, which adds a leap month about every three years. The placement of this leap month varies from year to year, and the name of the month is the same as the month preceding it.The Iranian calendar adds a leap day every four years as well, however every 6 or 7 years, the leap day is added on the fifth year instead of the fourth. The Iranian calendar, which only needs correction every 141,000 years, is more accurate than the Gregorian calendar, which needs correction about every 3226 years.Other examples include the Jewish (which also adds a leap month, Adar I), Hindu, Islamic, Baha'i (which adds a leap day to the last month every four years), and Ethiopian calendars. As far as I can tell, pretty much every country has a form of leap year.
Same as the us and pretty much every other devolved country