Hi Andreas,
I checked with your PHP and I could verify that en_GB and en_US are 
installed.
I wrote this in the Typo3 setup:
    config.sys_language_uid = 0
    config.language =
    config.locale_all = en_GB.utf8
    config.typolinkLinkAccessRestrictedPages = NONE;
No change. I detail a bit more in my reply to Xavier above.
Many thanks,
Denis