A new iPhone app called Word Lens promises to translate foreign words on the fly. How? Just by pointing the phone's camera at a sign written in another language.

"A few years ago I was in another country, and there was a sign I couldn't read and I thought, 'Why doesn't my cellphone do this?'," said Word Lens creator Otavior Good in a video on his company's website.

"So I decided to make a translator."

The idea has already proven popular, with a demonstration video posted to YouTube three days ago racking up almost 2 million views and Word Lens becoming one of the top travel apps around the world.

The app is free to download, but each language pack will set you back $5 a pop. Only one pack is available at launch, for translations between English and Spanish.

Mr Good and colleague John DeWeese said they were working on creating European language packs first, but would eventually "get all the way across the globe".

Sydney freelance business analyst David Ludvik said he would have loved to have used the app during his last tip to Spain in 2008.

"The amount times that there were signs, and it's kind of hard to look up every single word, and it's hard to know which words in a sentence — verbs and nouns and that kind of thing — when you’re not familiar with the language," he told news.com.au.

"It's kind of time consuming translating a lot of useless words when all you want to do is get the point."

Word Lens uses optical character recognition technology to translate words on the fly. Mr Ludvik said he wished it was available in other languages as well.

"In fact I want there to be one for Japanese," he said.

"I'm moving to Japan — and that’s a whole other kettle of fish because they’ve got four other alphabets that they use.

"There's Kanji Hiragana, Katakana and Romaji — Romanji uses roman letters, but that's not very common for the signs in the street, so to be able to hold up the phone and get the message would be completely amazing."

News.com.au took Word Lens for a test run and found the translation service didn't work quite as well as the promotional video would have you believe — but it does work.

The app doesn't respond well to movement and the words tend to jump, move and change shape as the camera shifts with your body.

Word Lens isn't the first app that uses the iPhone's camera to translate words, but it is the first that doesn't need a wireless internet connection to operate.

However don’t go throwing out all of your travel dictionaries just yet. The app only works for printed text, so you're on your own when it comes to translating hand-written notes or signs.