It's not a language pack problem because the system default (en-US) is used throughout.
Fortunately, I have solved the problem and now have an explanation. It's the result of the combination of several contributing factors:
1) My being new to DNN and both host/portal administration, as well as under the gun to use this holiday weekend to get a lot done before I leave on a business trip at the end of this holiday weekend.
2) Some default message content (for example, in EMAIL_USER_REGISTRATION_ADMINISTRATOR_BODY.Text in the file GlobalResources.resx) that was confusing and mistaken by me as the message to New User rather than message to Portal Administrator.
3) Delivery of the Portal Administrator message to admin email address but NON-delivery of the New User message to the new test user email address - simultaneously from the same web server hosting the new DNN portal - and my not realizing that simultaneous messages were supposed to be sent to both Portal Admin and New User and received by both of them (which in this case was me acting in both roles for test purposes).
To prevent any further confusion or problems for any other new Portal administrators, I recommend the following:
1) Rewrite all message templates in GlobalResources.resx so each message content has clear and unambigous content in both subject and body identifying the role of recipient especially whether intended for the Portal Administrator or the New User. I am certainly rewriting my own installed copy of this file to prevent any further confusion. Ideally future official DNN releases will have default message content that identifies both the role and the name of the person so that there can be no possible confusion.
2) Advise all new Portal Administrators to test new portals with test users and test email addresses on domains for which the hosting web server has proven email sending capability, ie, the email server hosting the test user email address must not be blocked or prevented from relaying by some intervening ISP's blacklists.
So that solves the DNN new user verification problem. Now the big problem I have to solve is why email has not been relayed to the mail server hosting the test user email address that never received the messages with the verification codes for login to DNN.