I have the same problem. I have tried to use different versions of php without luck.
$ locale -a
C
C.UTF-8
en_US.utf8
POSIX
I am using Debian buster, Apache/2.4.37 (Debian) OpenSSL/1.1.1 and PHP Version 7.2.9-1
The log reads:
{“reqId”:“NNBkyC8CFFrVwXPrakIx”,“level”:3,“time”:“2018-11-15T09:30:02-05:00”,“remoteAddr”:"",“user”:"–",“app”:“PHP”,“method”:"–",“url”:"–",“message”:“You are using a fallback implementation of the intl extension. Installing the native one is highly recommended instead. at /var/www/owncloud/lib/composer/patchwork/utf8/src/Patchwork/Utf8/Bootup/intl.php#18”}
I also have php7.2-intl installed
Package: php7.2-intl
Version: 7.2.9-1
New: yes
State: installed
Automatically installed: no
Priority: optional
Section: php
Maintainer: Debian PHP Maintainers team+pkg-php@tracker.debian.org
Architecture: amd64
Uncompressed Size: 524 k
Depends: php-common (>= 1:35), ucf, php7.2-common (= 7.2.9-1), libc6 (>= 2.14), libgcc1 (>= 1:3.0), libicu60 (>= 60.1-1~), libstdc++6 (>= 4.9)
Provides: php-intl
Description: Internationalisation module for PHP
This package provides the Internationalisation module(s) for PHP.
PHP (recursive acronym for PHP: Hypertext Preprocessor) is a widely-used open source general-purpose scripting language that is especially suited for web
development and can be embedded into HTML.
Homepage: http://www.php.net/