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If you don't call AlertDialog.Builder.setIcon() and AlertDialog.Builder.setTitle(), then your custom dialog will not show the built-in/default title View. In this case you are able to add your custom title View:
AlertDialog.Builder.setView(View view)
As soon as it is you who create this View it is possible to implement any type of alignment.
You've got some starting tips here for modifying the title of a dialog: Android - change custom title view at run time Don't know if it can be centered(haven't tried), but if it's a custom View I guess it's very possible.