I finally found the password specifications in the settings of the password field CB/field management/ password / validation -> here , there is a list where we can choose (12 words, 6 words + special characters...). The default value is "empty", which should result in using Joomla general passwords settings, but, when this list box is on empty, actually it chooses (6words+ special...).
When changing password rules, we also must not forget the modification of the language override of _UE_VALID_PASS (plugin management/ default...).