I think blocking the users from posting during a certain period is a lot easier than blocking them from posting foreign languages. This method is only involved with account activation while later is involved with content filtering. We have seen users temporarily suspended by mods in the past because they violated CC terms.
Another way to restrict multiple spamming threads during a short period is to require a minimum amount of time between new threads. 2 to 4 hours are reasonable. Normal users would not need to create multiple threads in a day.