Hi Bastian,
thank you for your hint. I tried it with my http component, but I get
# Warning: preg_match_all() expects parameter 2 to be string, array given in .../Data/Temporary/Development/Cache/Code/Flow_Object_Classes/Neos_Flow_I18n_Utility.php line 52
So instead of
if (preg_match_all(self::PATTERN_MATCH_ACCEPTLANGUAGE, $acceptLanguageHeader, $matches, \PREG_PATTERN_ORDER) !== false) {
The detectLocaleFromHttpHeader() method is missing type hints but it expects a string.
So instead of $httpRequest->getHeader('Accept-Language') try with $httpRequest-> getHeaderLine('Accept-Language')