There are more than 3000 languages in the world. But let'e be generous and say that only the 20 major languages are seen in the Monastery. Could you imagine how to deal with such a Babel?
I'd wait and see if a babel actually occurred. If it did I would (or rather, I would encourage pmdev to :-) tag posts with the language and allow users to filter posts by the languages they're interested in.
How do you approve posts you don't understand? If it was posted to PerlMonks Discussions, for example, how do you know that it should be approved/moved to Meditations or SOPW?
I wouldn't approve posts I don't understand. Just like I don't approve posts on technical topics I am not familar with, or posts that I cannot understand because English is not a language the writer can use. People who do understand it will approve it, or it won't get approved.
How do you address people to the FAQs or the instructions on how to ask questions, which are the basic principles of our community? Are we going to translate each piece of relevant information in every language that shows up? It took about three years to get those documents to the actual state, in one language only. How do we plan to deal with the additional languages?
As with any community led process those with the knowledge will translate - or it won't get translated. Translation is also a less time consuming task that writing.
How do you consider a post for editing, deletion, promotion, if you don't know what is it talking about?
I wouldn't consider a post if I didn't understand it. Just like I don't consider posts on technical topics I am unfamiliar with. People who do understand it will do the consideration, or it won't happen.
Yes, perlmonks in other languages is going to be less useful than perlmonks in English - just because there are more perlmonks with English as a common tongue. However, I don't see that this is going to make perlmonks as a whole less useful.
To me all this talk of principles and rules in premature. Let's wait to see if an actual problem occurs. I doubt it will because perlmonks is useful because of the community and the majority of the community has English as a lingua-franca. In my opinion allowing other languages will not change this.