Review visibility of get_dismiss_i18n_message_button()

[jrfnl]

From #54

there are two @access private tags remaining. These are set for public methods.
For those, it should be decided whether the method visibility is correct and if not, the method visibility should be changed.
Either way, the tag should be removed after this has been examined.

In both cases, this is about the get_dismiss_i18n_message_button() method.