The answer to the question of which are the most common languages is actually a little bit complex. Thousands of languages are spoken all over the world, and a number of rubrics could be used to determine which are the most common. As a result, estimates of the most common languages can sometimes vary considerably. As a general rule, Mandarin Chinese, Spanish, English, Bengali, and Arabic tend to occupy the top five spaces on the list, in varying order, but Hindi, Urdu, Russian, Portuguese, Japanese, German, and French also rank very high.
One way to look at the most common languages is to determine the number of native speakers. Mandarin Chinese wins this contest hands down, with over one billion native speakers as of 2005. Trailing behind, Hindi, Spanish, and English have around 330 million native speakers each, and Bengali, Arabic, and Russian have around 170 million native speakers.
However, just looking at the number of native speakers does not provide a complete picture. Many languages have relatively small numbers of native speakers, but huge numbers of secondary speakers. English is a classic example, with people all over the world learning English to do business, engage in diplomatic communications, and to communicate with people from around the world. While the top five languages remain fairly consistent once the numbers of secondary speakers are taken into account, English usually jumps into second place, with almost half a billion native speakers.
Another way to look at the most common languages around the world is where languages are spoken. Some have large numbers of speakers, but are only spoken in a handful of countries. Others are spoken in numerous countries, and not just in numerous countries, but in nations all over the world, rather than a cluster of nations limited to a small geographic region. English, for example, is the official language in over 50 countries around the world. English is also commonly the official language used by international organizations and international businesses such as banks.
Some people also consider socioeconomic power when evaluating language usage around the world. Portuguese, for example, is often in the top 10 list of most commonly spoken languages, but the nations in which this language is used are not widely associated with socioeconomic power, meaning that the language may have less clout than languages like Japanese and German, which are often ranked below Portuguese in terms of number of speakers.