Littlegolden Well, from what I understand, you would benefit greatly from a mass post/account deleter extension, as well as a somewhat intelligent rapid -fire posting detection extension.
The first one is tricky - although it is not difficult to create such an extension, it's misuse could lead to grave consequences. Personally, in the near future I might be creating an extension that automatically erases users who never validated their mail based on a set of rules. It's something I need given that I have a rate of almost 2% incorrectly typed academic emails, something that might prevent future users from registering with their own account if it was previously mistakingly entered. You might then be interested in giving it more functionality, such as deleting permabanned users and their posts.
For now, you can probably go to your database via SSH and run SQL queries that will delete the spam, but I'd recommend you talk to someone more qualified than me on how to do it.
The second one can already happen using rule based spam filters. I'm pretty sure Akismet covers rapid-fire posting. The only question is if their plan is acceptable for you (they do have free plans, but they also have paid plans). A more lightweight extension could be written, of course, too, but I don't know of anyone that's currently interested in doing it.
Personally, my current line of work revolves heavily about spam detection. It's something that's insanely tricky given today's software and hardware capabilities. The algorithms we have are trash and the knowledge we have about language itself is very poor. Effectively combating spam requires intricate knowledge of not only its patterns, but also the techniques for detecting them. To answer your question on what spam is harder to detect, most systems are trained on english data, so naturally detecting english spam is usually the easiest.
What I would recommend you to do is that you focus on solving the problem with Akismet for now, because it's probably the best fit given your problems. Better solutions will without a doubt include more complex systems that will have to combine good performance with low overhead, and those are far, far away.
