WeChat also allows users to chat either by audio or video, and Rochfort says he has found the app's ability to translate text into other languages, including Thai, a great help and a valuable learning aid.

With WeChat, which was launched in 2011, users - as long as they have an Internet connection - can display pictures, video and written material that they think contacts may find interesting.

They can book taxis, buy bonds, shop, order food and almost anything else and pay for all these things by linking the WeChat account to a bank account. Accounts can be set up by individuals or corporate entities.

The first research report about WeChat, released by owner Tencent late last year, showed that Internet usage over WeChat generated 95.2 billion yuan ($14.6 billion; 13.2 billion euros) in revenue; and 11 billion yuan worth of daily consumption items were bought.

The newspaper USA Today said recently that WhatsApp, a popular communication app in the West, now has 900 million monthly active users; Twitter has a little more than 300 million; and Instagram, the photo and video-sharing app that Facebook owns, also has about 300 million.

Mobile Messaging Apps: Global User Forecast, a report by eMarketer, a digital industry research firm, says more than 1.4 billion consumers worldwide were expected to use a mobile messaging app last year, and it forecasts the number will grow to 2 billion by 2018.

A recent Forbes article expects average monthly users on WhatsApp to increase to nearly 1.3 billion by the end of 2020. It also forecasts WhatsApp's average revenue per user will be around $4 by 2020, which could yield revenues of around $5 billion.

WeChat has a far wider range of functions than an instant-messaging app, and it differs from Twitter and Facebook, where content can be made available to very large audiences, in that communications are usually restricted to individuals who know one another. Exceptions to this are its People Nearby and Shake functions, which allow users to make contact with strangers.

Charles-Edouard Bouee, global CEO of the consulting firm Roland Berger, says WeChat brings together the features found in other apps.