My fellow guru Seavixen said it all here above. Basically I have nothing to add, but here you get detailed answers for your questions.
But do u now however admit that one can change a English bios to a German bios and vice versa?
Yes, although it's useless regarding what you want to achieve and has nothing to do with the language of your windows setup. Only things that will change language are BIOS setup screen and some of the so called POST information shown on screen when PC is booting. These have nothing to do with the language of the Windows.
And if u are sertain about this satement u made that it is not the bios that is the determinating factor for the language that the computer uses for everything then what is the determinating factor for language then?
Yes, I am sure. I consider myself as a language expert when it comes to Windows. Geeks here know I am not a modest person so let's say I know about everything there is to know about Windows language changes and language packs

. Just do advanced search here at SF searching my posts using "Language pack" as search criteria and you can see it yourself. OK?
The decisive factor is the language of the Windows DVD you have bought, or the language of a pre-installed Windows if you got your Windows already installed with PC. There's no way you can change this language in Windows 7 Starter, Home Basic, Home Premium and Professional editions.
In Windows 7 Ultimate and Enterprise editions it is possible to change the display language completely using so called
Language Packs. This change can be made individually and separately for each and every user account. For instance all my PCs have user accounts in my native Finnish and Swedish, as well as in English and German:
Notice that in some areas computers with pre-installed Windows let you select the language of the operating system when first time
OOBE boot is made, when computer is first time set up. For instance in my native Finland all new PCs let you select between Finnish, Swedish and English. Once this selection is made it can not be reverted, even if you do a factory reset the language remains as that which was selected during the first OOBE boot.
Also in some areas you can buy Windows DVDs with more than one language. Then it is a simply question of selection when installing Windows.
and if proof can be had that this is true, how do u apply a system wide language change to a computer without using non~native software or other utilitys?
I am not bothering to find more proof to you. If you will not believe me and my expertise in multilingual Windows, feel free to search Internet or ask elsewhere.
thank u .. id really like to figre this out with all of your help and be able to properly setup a computer in a language I can compute.
You have two choices:
1. Buy Windows 7 DVD or ISO in language you'd like to have and use it to reinstall
2. Use
Windows Anytime Upgrade to upgrade your Home Premium to Ultimate, then using Windows Update download and install language packs of your preferred language
Any way if the bios change from german to english does succeed by flashing...! then u all say that windows wont adapt? So what would happen if one installs a new harddrive or simply format the old drive after the flashing of the bios completed ... will the computer then accept the new language of the system and give one an option for that language when windows setup is in progress?
No. Flashing BIOS and changing BIOS language, then reinstalling Windows does not change the language of Windows. The decisive factor is not the BIOS language but the language of your Windows install media.
Kari