Prestashop v. 1.7.7.1 exige une version de ICU récente. Il est très simple de régler le problème :

https://github.com/PrestaShop/PrestaShop/issues/24538

There is a problem with constant INTL_IDNA_VARIANT_UTS46 in the file « src/Core/Util/InternationalizedDomainNameConverter.php »
It needs to be modified as follows. The constant INTL_IDNA_VARIANT_UTS46 needs to be converted to int type explicitelly by intval() on the line 47.

FROM:
return $parts[0] . ‘@’ . idn_to_utf8($parts[1], 0, INTL_IDNA_VARIANT_UTS46));
TO:
return $parts[0] . ‘@’ . idn_to_utf8($parts[1], 0, intval(INTL_IDNA_VARIANT_UTS46));

https://www.prestashop.com/forums/topic/1042289-r%C3%A9solu-plus-de-backoffice-apres-mise-a-jour-de-1765-vers-1771/