There is a policy Microsoft has about this issue.
If your company is an International Corporation, and if the company has a Corporate License from Microsoft, your company can provide you with a new XP install CD in English.
Or a special pack that will convert the present installation. Due to the numerous updates that have taken place, the service pack for the conversion may no longer be usable.
Otherwise, as far as I know, the is no quick easy way to convert the entire Windows OS over to another Western language. But you can get applications that work in another language.
But, there is a Turkish Microsoft Windows sold as the Windows XP Pro MultiLingual for $300 and I would think that is NOT what you have and you do not want to shell out that kind of money.
Sorry, I am not much help.