[squid-users] Squid 4.4: SSL/certification error messages not displayed with non-english error_directory

[info at schroeffu.ch]

Changing the error_directory to non-english like german or italian, the ssl bump error messages like "expired certificate" or "self signed certificated" are not showing anymore. Browser is just displaying an ugly error 503. But, other error messages like "access denied" are displayed properly, also tested with German and Italian.

#error_directory /usr/share/squid/errors/German
#error_directory /usr/share/squid/errors/Italian

How do I debug that properly to raise a bugeport if required?

Squid Version: 4.4-1 (from Debian unstable on Ubuntu 18.04 Server, recompiled with openssl)
Squid Langpack Version: Version: 20170901-1 (from Debian unstable on Ubuntu 18.04 Server)
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