Solution:
WordPress and MediaWiki are independent applications and one can not expect a plugin written for one to be directly portable to the other. If you are lucky some of the code may be reusable but it will not be as simple as a cut and paste. The two application has different ways of doing things.
1) No, WordPress will not be able to understand such tags. WordPress can be made to understand MediaWiki style markdown tags with additional plugins but I do not recognise the tag example you highlight.
2) I think your current approach is sound, you will need to understand what the MediaWiki code is doing and re-create this within a WordPress plugin. I doubt there is a short cut to this other than taking some time to get to grips with WP plugins. If you enjoy coding and writing plugins thin this is time well spent. Being able to customise WordPress is very useful.
3) Other than re-coding it yourself the other option would be to see if there is a WordPress plugin that does what you are looking for. Your question does not detail what exactly the functionality is that you are trying to add.
Having written plugins for both MediaWiki and WordPress I have found the easier more enjoyable to work with.