Fher,
The values you are searching for are stored in the following locations:
Enter your User Name below
DNN v.4.5.5, Directory\File: ~\admin\Security\App_LocalResources\Signin.ascx.yy-XX.resx
DNN v.4.6.0 and up, Directory\File: ~\App_GlobalResources\SharedResources.yy-XX.resx
Enter your Password below
DNN v.4.5.5, Directory\File: ~\admin\Security\App_LocalResources\Signin.ascx.yy-XX.resx
DNN v.4.6.0 and up, Directory\File: ~\App_GlobalResources\SharedResources.yy-XX.resx
DNN v.4.6.2 and up, Directory\File: ~\DesktopModules\AuthenticationServices\ActiveDirectory\App_LocalResources\Login.ascx.yy-XX.resx
Password:
DNN all versions, Directory\File: ~\admin\Portal\App_LocalResources\Signup.ascx.yy-XX.resx
DNN up to v.4.5.5, Directory\File: ~\admin\Security\App_LocalResources\AuthenticationSettings.ascx.yy-XX.resx
DNN up to v.4.5.5, Directory\File: ~\admin\Security\App_LocalResources\Signin.ascx.yy-XX.resx
DNN all versions, Directory\File: ~\admin\Users\App_LocalResources\Password.ascx.yy-XX.resx
DNN all versions, Directory\File: ~\admin\Users\App_LocalResources\User.ascx.yy-XX.resx
DNN v.4.6.0 and up, Directory\File: ~\App_GlobalResources\SharedResources.yy-XX.resx
DNN all versions, Directory\File: ~\controls\App_LocalResources\User.ascx.yy-XX.resx
DNN v.4.6.2 and up, Directory\File: ~\DesktopModules\AuthenticationServices\ActiveDirectory\App_LocalResources\Login.ascx.yy-XX.resx
DNN v.4.6.2 and up, Directory\File: ~\DesktopModules\AuthenticationServices\ActiveDirectory\App_LocalResources\Settings.ascx.yy-XX.resx
DNN all versions, Directory\File: ~\Install\App_LocalResources\Installwizard.aspx.yy-XX.resx
User Name: & Username:
DNN all versions, Directory\File: ~\admin\Portal\App_LocalResources\Signup.ascx.yy-XX.resx
DNN up to v.4.5.5, Directory\File: ~\admin\Security\App_LocalResources\AuthenticationSettings.ascx.yy-XX.resx
DNN all versions, Directory\File: ~\admin\Security\App_LocalResources\SendPassword.ascx.yy-XX.resx
DNN up to v.4.5.5, Directory\File: ~\admin\Security\App_LocalResources\Signin.ascx.yy-XX.resx
DNN all versions, Directory\File: ~\admin\Users\App_LocalResources\User.ascx.yy-XX.resx
DNN all versions, Directory\File: ~\App_GlobalResources\SharedResources.yy-XX.resx
DNN v.4.6.0 and up, Directory\File: ~\App_GlobalResources\SharedResources.yy-XX.resx
DNN all versions, Directory\File: ~\controls\App_LocalResources\User.ascx.yy-XX.resx
DNN v.4.6.2 and up, Directory\File: ~\DesktopModules\AuthenticationServices\ActiveDirectory\App_LocalResources\Login.ascx.yy-XX.resx
DNN v.4.6.2 and up, Directory\File: ~\DesktopModules\AuthenticationServices\ActiveDirectory\App_LocalResources\Settings.ascx.yy-XX.resx
DNN up to v.4.6.2, Directory\File: ~\DesktopModules\Forum\App_LocalResources\Forum_UserSettings.ascx.yy-XX.resx
DNN all versions, Directory\File: ~\Install\App_LocalResources\Installwizard.aspx.yy-XX.resx
Note 1: yy-XX is the culture code (i.e., en-GB, es-ES, etc.), for US english yy-XX does not exist.
Note 2: If you are not sure about which message to change, it may help to make an iterative testing.
Note 3: You should change this values under the menu option Host-Languages-Language Editor. For further recommendations on how to use the Language Editor, please check my post at this thread: http://www.dotnetnuke.com/Community/Forums/tabid/795/forumid/77/threadid/215279/scope/posts/threadpage/1/Default.aspx
HTH.
Saludos,
Alejandro.