You can control the display format of dates, numbers etc. by setting the Language property of the affected textboxes (or the entire Report). If you don't set this property then these types of data are rendered using the culture settings of the Report Server (in your case this will be U.S. formats).
To make your report responsive to the culture setting of the client PC you can set the Language property (of the whole Report or individual text boxes) using the expression
=User!Language
More information: http://technet.microsoft.com/en-us/library/ms159642.aspx