I fully agree with what Jeff said - and I don't have much else to add regarding your particular experiment. Thanks for coming and sharing your experience, this is valuable insight.
I want to talk about the business of multiple accounts in general, because it's important for folks to know some stuff.
Most importantly, note that what you did was technically quite difficult, because our system is engineered around the concept of a single account with many linked profiles. A single slip of using the wrong email or wrong credentials in the wrong place most likely would have triggered an automatic merge of your accounts - and there's nothing that we could have done to prevent it. We do not technically support users having multiple accounts, but we don't disallow it for the most part.
That said, you don't need any particular permission from us to create a second account, for whatever reason, provided that you don't do anything that you couldn't otherwise do with a single account. This includes voting for your own posts, starring your own messages in chat, coordinating flagging between the two, etc. You should also strongly consider not creating a secondary account for the express purpose of contributing lesser quality posts without fear of reproach - that's going to bring an uncomfortable level of moderator attention on you, and quite possibly out you.
You're of course welcome to contact us if you wish, but there's no need to do so if you just intend to contribute positively, just under a different name. If you're planning anything even remotely strange, then yes - please do get in touch.
The Stack Exchange community team routinely creates anonymous accounts to judge the experience that any reasonably articulate individual would enjoy, or perhaps endure, depending on the site. New community managers are often not announced for the first few weeks of their employment specifically to give them the opportunity to do this.
Valid reasons for maintaining independent accounts while contributing include:
The desire to separate recreational or faith-based contributions from your more professional profiles on certain sites.
The desire to not be associated with contributions that entail revealing more about yourself than you're comfortable doing
The desire to avoid embarrassment by revealing that you don't know something that you feel you probably should (note, this is going to be key if a site in Japanese is going to work)
The desire to do exactly what you did, experience the site as a new user
Regarding the last bullet, I don't think it's possible to experience the site as a new user completely, especially after being immersed in our culture for so long. You simply aren't going to make many mistakes that new users tend to make, which drastically reduces the chances of having critical, or even negative interactions with others. That's something that you need to think about.
If you decide to create a new account, just be certain that you don't do anything with it that you could not otherwise do with a single account - or you will likely find yourself on the wrong end of a moderator's action, which could include the removal of one of the accounts and a hefty suspension.
And remember, if you're outed - even accidentally by the system doing what it's programmed to do, that's just the way it goes, it's a risk you need to accept.
