The statement is false. While the company can set a default locale to US English, users have the ability to change their personal locale settings to suit their individual preferences.

If your company's fiscal year follows the Gregorian calendar, you do not need to use Custom Fiscal Years. Standard Fiscal Years are used for companies that follow the Gregorian calendar, which runs from January to December. Custom Fiscal Years are only necessary if your company uses a different fiscal year structure.

In order to enable the multi-currency feature in Salesforce, you must contact Salesforce.com. This is because enabling multi-currency involves significant changes to the organization's settings and impacts various features within Salesforce. Such changes require Salesforce's intervention to ensure proper configuration and functionality.

Advanced Currency Management effectively allows you to 'lock' the converted amount on closed opportunities by managing dated exchange rates. This feature enables users to map a conversion rate to specific date ranges, ensuring that the conversions remain accurate and fixed for closed opportunities in Salesforce.

User interface settings are indeed global settings and apply to all users of an organization. These settings control aspects of the user interface that affect how all users view and interact with the features available within the interface.