Account deactivation warning is not clear enough

### Description

It seems that the warning shown when a user deactivates their account is not clear enough. Specifically, it seems that it is not always clear that the user id can not be registered. Possible reasons include confusing terminology (what is a user ID?), difficulty understanding the language (if non-native), lack of attention, etc.

Perhaps some sort of generally understood warning icon could be added to draw attention to the fact that something potentially bad is about to happen.

Also, like in some system, perhaps require the user to type in their user id, as that may strengthen the point that what they are about to do is really, really important.

Finally, the key part of the text could perhaps be in bold.