WordPress.org

Is this plugin the ultimate spam-bot protection?

Of course not, but it is a great additional protection against them.

Can I put some HTML into the new link?

No! The only valid characters are [a-zA-Z0-9_-] and in general any character valid in an URL-encoded string.

Why isn't Custom Registration Link translated in my language?

Most probably because nobody submitted a translation for your language yet. But you can help. Read our guide for plugins translators at http://www.gabsoftware.com/tips/a-guide-for-wordpress-plugins-translators-gettext-poedit-locale/