According to this https://help.salesforce.com/apex/HTViewHelpDoc?id=customize_rename.htm to rename labels for standard fields you have to Be designated as a translator. Is this everyone who have System Administrator profile or who?
A Designated translator is a user with the Manage Translations permission assigned for a specific language. This can only be done after the Translation Workbench has been enabled. System Administrators get this permission by default. The users will also need to have the 'View Setup and Configuration' privilege assigned to them.
To assign translators for this language, select them from the Available List and click Add. If you don’t see the member you want to add, enter keywords in the search box and click Find.