Breaking: #96889 - Require PHP mbstring and intl

See Issue #96889

Description

The two PHP extensions mbstring and intl are required to be loaded when running TYPO3 v12.

mbstring is a common extension that is either compiled directly into PHP or available as standard package in all distributions and operating systems. Similar for intl. While there are symfony packages that mimic these extensions partially if not available, these “polyfill” packages are slower, and most importantly, they implement only parts of the native extensions. To further improve TYPO3 character set and internationalization handling, the system needs the full functionality.

Impact

System environments not providing these PHP extensions may fail.

Affected Installations

The install tool “Environment Status” and the reports module notify about missing PHP extensions, and it is shown during the installation process.

Migration

Provide the extensions in the PHP.

A debian / ubuntu based Linux host typically install such packages with a command similar to this:

sudo apt install php8.1-mbstring php8.1-intl