Just one question, if i wan't to create new language, does i only need to translate english.xml in for example croatian, or i need to do some more customization?

You need to create a new xml file for the language.

- For Example create a file called croatian.xml
- Copy the complete content from the english.xml to the croatian.xml file
- Now you need to modify the language name and language code

now i have this problem
Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

If i add croatian xml, do i have to configure something more? Because when i add it i have probem in Board Settings and Languages tabs in admin part of the page ... Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

this is the stack
[NullReferenceException: Object reference not set to an instance of an object.]
YAF.Core.StaticDataHelper.Cultures() +840
YAF.Pages.Admin.languages.BindData() +17
YAF.Pages.Admin.languages.Page_Load(Object sender, EventArgs e) +289
System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35
System.EventHandler.Invoke(Object sender, EventArgs e) +0
System.Web.UI.Control.OnLoad(EventArgs e) +99
System.Web.UI.Control.LoadRecursive() +50
System.Web.UI.Control.LoadRecursive() +141
System.Web.UI.Control.LoadRecursive() +141
System.Web.UI.Control.LoadRecursive() +141
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +627

try with this one

hahaha , what was the problem???

all is working fine , ablle to locate the problem