Apple (NASDAQ:AAPL) might have disappointed the hordes of people dying to get their hands on an iPhone 5 when it announced the new iPhone 4S on Tuesday, but the company still managed to impress with new apps. Particularly impressive is Siri, Apple’s new voice-command app that lets you literally talk to your iPhone. Need to know how bad traffic is in your area? Just ask the phone, and Siri will give you real-time data on traffic outside.

However, Apple forgot the cardinal rule of language-based technology: If you build it, your audience is going to make lewd jokes with it. And Apple’s new app made it all too easy for people to turn it into a joke, considering what Siri sounds like in Japanese. Here’s a hint: The iPhone 4S almost certainly will be Sir Mix-a-Lot’s favorite smartphone.

To Japan, the name Siri sounds almost identical to ?, pronounced shiri. Shiri is a colloquialism for — in the politest possible sense — buttocks. Its proper usage, however, is crude. As Yoree Koh of The Wall Street Journal put it, the comparable term in English rhymes with “crass.” Compliments for Apple’s major new technology, likely to be the focus of marketing campaigns across the world, will make the speaker sound like a cat-calling construction worker in Japan.

Shortly after Siri was announced, both “Siri” and “shiri” became trending topics on Twitter in Japan. Google Japan searches for Apple’s new voice recognition software had the search engine asking users if they actually were looking for “shiri,” and it isn’t difficult to imagine what the image search returned on those queries.

Given Apple’s flair for branding, it’s surprising that the company didn’t know about this potential gaffe before announcing Siri to the world. Japan is, after all, a major market for the company.

The iPhone itself was the first major smartphone success in the country, capturing 72% of the Japanese smartphone market by the middle of 2010. Although Google (NASDAQ:GOOG) Android phones have narrowed the gap in 2011, diminishing Apple’s share of the total market to 38%, Japan still is a major market for Apple. The Cupertino, Calif.-based company shipped 3.23 million iPhones in the country in the last fiscal year.

When your biggest mobile operating system competitor has crushed your lead in less than 12 months, it probably isn’t the best idea to name a major new feature of iOS after butts. This is Apple, though. The iPhone 4S and Siri should prove as popular as previous Apple mobile products — named after someone’s rear or not.

As of this writing, Anthony John Agnello did not own a position in any of the stocks named here. Follow him on Twitter at @ajohnagnello and become a fan of InvestorPlace on Facebook.