Fatal error on Ubuntu 20.04 / PHP 7.4

Description

When installing fusiondirectory via the official debian packages on Ubuntu 20.04, I get the following error:

Fatal error: cannot instantiate class 'Language' - try running 'fusiondirectory-setup --update-cache' to fix this.

Distribution Name and Version

Ubuntu 20.04.1 LTS

FusionDirectory Version

1.3 (Package version 1.3-2)

PHP version used

7.4.3 (Package version 7.4.3-4ubuntu2.2)

Origin of php packages

Distribution packages of Ubuntu 20.04:

php-cas/focal,now 1.3.8-1 all [installed,automatic]
php-common/focal,now 2:75 all [installed,automatic]
php-curl/focal,now 2:7.4+75 all [installed,automatic]
php-fpdf/focal,now 3:1.8.1.dfsg-2 all [installed,automatic]
php-gd/focal,now 2:7.4+75 all [installed,automatic]
php-imagick/focal,now 3.4.4-4 amd64 [installed,automatic]
php-imap/focal,now 2:7.4+75 all [installed,automatic]
php-ldap/focal,now 2:7.4+75 all [installed,automatic]
php-mbstring/focal,now 2:7.4+75 all [installed,automatic]
php-xml/focal,now 2:7.4+75 all [installed,automatic]
php7.4-cli/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 amd64 [installed,automatic]
php7.4-common/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 amd64 [installed,automatic]
php7.4-curl/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 amd64 [installed,automatic]
php7.4-fpm/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 amd64 [installed,automatic]
php7.4-gd/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 amd64 [installed,automatic]
php7.4-imap/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 amd64 [installed,automatic]
php7.4-json/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 amd64 [installed,automatic]
php7.4-ldap/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 amd64 [installed,automatic]
php7.4-mbstring/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 amd64 [installed,automatic]
php7.4-opcache/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 amd64 [installed,automatic]
php7.4-readline/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 amd64 [installed,automatic]
php7.4-xml/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 amd64 [installed,automatic]
php7.4/focal-updates,focal-security,now 7.4.3-4ubuntu2.2 all [installed,automatic]
php/focal,now 2:7.4+75 all [installed,automatic]

Steps to Reproduce

1. Get a fresh Ubuntu 20.04 installation
2. Add fusiondirectory deb sources to /etc/apt/sources.list.d/fd.list: deb http://repos.fusiondirectory.org/fusiondirectory-current/debian-stretch stable main
3. Install fd with nginx and without apache2: sudo apt install nginx apache2- apache2-bin- fusiondirectory
4. Modify default nginx config:

root /usr/share/fusiondirectory/html;
index index.php;
location ~ \.php$ {
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
}

5. Reload nginx: sudo systemctl reload nginx.service
6. Visit the webserver in a browser: http://10.0.0.245/

Expected behavior:

The webserver redirects to (runs) the setup wizard (setup.php).

Actual behavior:

The webserver only returns:

Fatal error: cannot instantiate class 'Language' - try running 'fusiondirectory-setup --update-cache' to fix this

Trace[1]: function spl_autoload_call	File: /usr/share/fusiondirectory/html/index.php (Line 189)	Type: -
Arguments: "Language"

Reproduces how often: every time

Additional Information

I'm not entirely sure if Ubuntu is fully supported, but it states so here.