[TYPO3] Localized items don't show up

[Lars Kappert]

With the cc_debug extension installed, I can see the sys_language_uid is
always equal to 0 (zero). With something like:
debug($GLOBALS['GLOBALS']['TSFE']);

I am not able to set it in my template with
sys_language_uid = 1 or
config.sys_language_uid = 1 or
page.config.sys_language_uid = 1

for the default l10n-config. Nothing seems to affect the
sys_language_uid.

Can anybody tell me what I am doing wrong?