when running install.php (after recently upgrading my php and possibly missing some php extensions), I get:
Warning: The intl PECL extension is not available to handle Unicode normalization, falling back to slow pure-PHP implementation.
If you run a high-traffic site, you should read a little on Unicode normalization.
*Fatal: PHP must be compiled with support for the iconv extension.*
ext-iconv should be added in composer.json as a requirement and intl as suggested.