Just to clarify my previous message a bit more, what I was trying to say last time is that changing the server language rule doesn't change anything when it comes to spam. We already get spammers posting in all sorts of languages, those sorts of accounts are never trying to follow forums rules and they're certainly not going to be concerned about keeping things in English while they try to get people to click strange links. I agree that it's generally very easy to distinguish spam messages regardless of the language.
The issues that can arise from moderating messages in languages we aren't fluent tend to be much more nuanced. For example, something like Google Translate may let us see if someone is using a curse word in another language, but it doesn't give us an understanding of modern slang that exists in that language. An example was given in this thread of someone asking for asking for help. There are lots of different ways someone could ask for help; they could be polite or they could rude and abrasive to those attempting to help them. When we moderate messages in English, it's easy to understand when someone might need a gentle reminder of the rules.
None of this is not to argue against the original suggestion, I just wanted to expand on my last message. The staff team is discussing this one, and we are considering a few other small updates to the rules as well.