Labels for the web-client can be found in: webclient.properties The ones you are looking for are referenced from web-client-config.xml (look for the section <!– Dashboard layouts and available dashlets for the My Alfresco pages –>)
There is an override/extension mechanism for changing these values, http://wiki.alfresco.com/wiki/Adding_Custom_I18N_Strings as the wiki page says "A webclient.properties file can now be placed in the alfresco.extension package".