I changed language from English to Russian using "Manage" "Select language" and it works. We all need to learn Russian!
Now I tested version 1.19.1 and error message "Invalid date" persists.
My locale is cs_CZ.UTF-8, PasswordSafe version is 1.18.2.
PasswordSafe is nice application to store passwords. It is not possible modify entries now. In attached picture is error message "Invalid date"