Understanding Language, Locale, Time zone and Currency

Language- The default language that is selected for new users in the organization. This setting determines the language used for the user interface text and help.

Locale- This setting determines the format of dates, times, and names in Salesforce. individual users can set their personal locale, which overrides the organization setting.
The format used for dates, times, and names of people in Salesforce is determined by your Locale setting.
The Locale setting affects the format of date, date/time, and number fields, and the calendar. For example, dates in the English (United States) locale display as 06/30/2000 and as 30/06/2000 in the English (United Kingdom) locale. Times in the English (United States) locale display using a twelve-hour clock with AM and PM (for example, 2:00 PM), whereas in the English (United Kingdom) locale, they display using a twenty-four-hour clock (for example, 14:00).
The Locale setting also affects the first and last name order on Name fields for users, leads, and contacts. For example, Bob Johnson in the English (United States) locale displays as Bob Johnson, whereas the Chinese (China) locale displays the name as Johnson Bob.

Time Zone- Primary time zone in which the organization is located. A user's individual Time Zone setting overrides the organization's Default Time Zone setting.

Currency
International organizations can use multiple currencies in opportunities, forecasts, reports, quotes, and other currency fields.

The administrator sets the “corporate currency,” which reflects the currency of the corporate headquarters. The administrator also maintains the list of active currencies and their conversion rates relative to the corporate currency. The active currencies represent the countries in which the organization does business. Only active currencies can be used in currency amount fields.

Every user also has a personal currency, which is used as the default currency in his or her own quotas, forecasts, opportunities, quotes, and reports. Users can also create opportunities and enter amounts using other active currencies. Every lead, account, contact, opportunity, and case has a field that specifies the currency to use for all amount fields in that record. For example, you can set the Account Currency to “USD-U.S. Dollars” so that the Annual Revenue shows in dollars for one of your American accounts. All currency amounts are displayed in the default currency of the record as well as in the personal currency of the user.When you change the default currency of a record, currency amounts are not converted; they simply display with the new currency code.