[TYPO3] change language in own php script

[a owen]

Hi

I would like to change the language in typo3. In Typoscript it changes
the language with:

config.sys_language_uid = 1
config.language = de
config.locale_all = de_DE

so i thought that i could do the following in "class.tx_newloginbox.php"
in the main function, so that it would be displayed in german

$GLOBALS['TSFE']->config['config']['sys_language_uid'] = 1;
$GLOBALS['TSFE']->config['config']['language'] = 'de';
$GLOBALS['TSFE']->config['config']['locale_all'] = 'de_DE';

Are the variables wrong or am i approaching this wrong?

thanks for help
a owen