On multi-language sites, the account edit page has an additional tab for each language installed on the site front end. On each tab you can enter translations for the "translatable" fields. The translations are used on the front end of the site.
The text on the Details tab is used in the admin interface, regardless of the current admin language. Text from the Details tab is also used on the front end when a translation is not specified (i.e. when the translation of a field is blank).