When using team calendars for Confluence in conjunction with EN-US language pack and default language (in settings) is set to 'Automatically detect browser setting', the first day of the week displayed in the calendar remains Monday (which is default setting for english UK). When specifically setting language to English US, then the first day of the week displayed in the calendar changes to Sunday (which is setting for English US). Verified the browser setting (via developer tools when loading the page) header is passing in EN-US as language but the Calendar (when set to Automatically detecting browser setting) still displays Monday as first day of the week instead of Sunday.