Versuche zunächst die Sprache nicht über die Systemsteuerung, sondern über die Einstellungen zu ändern (Anleitung)
Wenn es nicht klappt, dann kannst du die Registry öffnen (Du musst als dieser User eingeloggt sein) und zum folgenden Registry-Schlüssel navigieren:
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Nls\Language
Info: Bevor du Registry änderst, erstelle einen Wiederherstellungspunkt, dann bist auf der sicheren Seite, falls doch etwas schief geht.
Dort findest du zwei D-Werte: Default und InstallLanguage
Doppelklicke darauf, es wird eine Zahl angezeigt, die für eine Sprache steht. Ändere die Zahl bei Beiden und trage 0407 ein, sie steht für Deutsch (Deutschland).
Speichere es und starte den PC neu.
Vielleicht wird es helfen, ich weiß es aber nicht.
Hier sind alle Sprachen-Codes:
0436 = "af;Afrikaans"
041C = "sq;Albanian"
0001 = "ar;Arabic"
0401 = "ar-sa;Arabic (Saudi Arabia)"
0801 = "ar-iq;Arabic (Iraq)"
0C01 = "ar-eg;Arabic (Egypt)"
1001 = "ar-ly;Arabic (Libya)"
1401 = "ar-dz;Arabic (Algeria)"
1801 = "ar-ma;Arabic (Morocco)"
1C01 = "ar-tn;Arabic (Tunisia)"
2001 = "ar-om;Arabic (Oman)"
2401 = "ar-ye;Arabic (Yemen)"
2801 = "ar-sy;Arabic (Syria)"
2C01 = "ar-jo;Arabic (Jordan)"
3001 = "ar-lb;Arabic (Lebanon)"
3401 = "ar-kw;Arabic (Kuwait)"
3801 = "ar-ae;Arabic (you.A.E.)"
3C01 = "ar-bh;Arabic (Bahrain)"
4001 = "ar-qa;Arabic (Qatar)"
042D = "eu;Basque"
0402 = "bg;Bulgarian"
0423 = "be;Belarusian"
0403 = "ca;Catalan"
0004 = "zh;Chinese"
0404 = "zh-tw;Chinese (Taiwan)"
0804 = "zh-cn;Chinese (China)"
0C04 = "zh-hk;Chinese (Hong Kong SAR)"
1004 = "zh-sg;Chinese (Singapore)"
041A = "hr;Croatian"
0405 = "cs;Czech"
0406 = "the;Danish"
0413 = "nl;Dutch (Netherlands)"
0813 = "nl-be;Dutch (Belgium)"
0009 = "en;English"
0409 = "en-us;English (United States)"
0809 = "en-gb;English (United Kingdom)"
0C09 = "en-au;English (Australia)"
1009 = "en-ca;English (Canada)"
1409 = "en-nz;English (New Zealand)"
1809 = "en-ie;English (Ireland)"
1C09 = "en-za;English (South Africa)"
2009 = "en-jm;English (Jamaica)"
2809 = "en-bz;English (Belize)"
2C09 = "en-tt;English (Trinidad)"
0425 = "et;Estonian"
0438 = "fo;Faeroese"
0429 = "fa;Farsi"
040B = "fi;Finnish"
040C = "fr;French (France)"
080C = "fr-be;French (Belgium)"
0C0C = "fr-ca;French (Canada)"
100C = "fr-ch;French (Switzerland)"
140C = "fr-lu;French (Luxembourg)"
043C = "gd;Gaelic"
0407 = "de;German (Germany)"
0807 = "de-ch;German (Switzerland)"
0C07 = "de-at;German (Austria)"
1007 = "de-lu;German (Luxembourg)"
1407 = "de-li;German (Liechtenstein)"
0408 = "el;Greek"
040D = "he;Hebrew"
0439 = "hi;Hindi"
040E = "hu;Hungarian"
040F = "is;Icelandic"
0421 = "in;Indonesian"
0410 = "it;Italian (Italy)"
0810 = "it-ch;Italian (Switzerland)"
0411 = "ja;Japanese"
0412 = "ko;Korean"
0426 = "lv;Latvian"
0427 = "lt;Lithuanian"
042F = "mk;FYRO Macedonian"
043E = "ms;Malay (Malaysia)"
043A = "mt;Maltese" 0414 = "no;Norwegian (Bokmal)"
0814 = "no;Norwegian (Nynorsk)"
0415 = "pl;Polish"
0416 = "pt-br;Portuguese (Brazil)"
0816 = "pt;Portuguese (Portugal)"
0417 = "rm;Rhaeto-Romanic"
0418 = "ro;Romanian"
0818 = "ro-mo;Romanian (Moldova)"
0419 = "ru;Russian"
0819 = "ru-mo;Russian (Moldova)"
0C1A = "sr;Serbian (Cyrillic)"
081A = "sr;Serbian (Latin)"
041B = "sk;Slovak"
0424 = "sl;Slovenian"
042E = "sb;Sorbian"
040A = "es;Spanish (Traditional Sort)"
080A = "es-mx;Spanish (Mexico)"
0C0A = "es;Spanish (International Sort)"
100A = "es-gt;Spanish (Guatemala)"
140A = "es-cr;Spanish (Costa Rica)"
180A = "es-pa;Spanish (Panama)"
1C0A = "es-do;Spanish (Dominican Republic)"
200A = "es-ve;Spanish (Venezuela)"
240A = "es-co;Spanish (Colombia)"
280A = "es-pe;Spanish (Peru)"
2C0A = "es-ar;Spanish (Argentina)"
300A = "es-ec;Spanish (Ecuador)"
340A = "es-cl;Spanish (Chile)"
380A = "es-uy;Spanish (Uruguay)"
3C0A = "es-py;Spanish (Paraguay)"
400A = "es-bo;Spanish (Bolivia)"
440A = "es-sv;Spanish (El Salvador)"
480A = "es-hn;Spanish (Honduras)"
4C0A = "es-ni;Spanish (Nicaragua)"
500A = "es-pr;Spanish (Puerto Rico)"
0430 = "sx;Sutu"
041D = "sv;Swedish"
081D = "sv-fi;Swedish (Finland)"
041E = "th;Thai"
0431 = "ts;Tsonga"
0432 = "tn;Tswana"
041F = "tr;Turkish"
0422 = "uk;Ukrainian"
0420 = "your;Urdu"
042A = "vi;Vietnamese"
0434 = "xh;Xhosa"
043D = "ji;Yiddish"
0435 = "zu;Zulu"