A number of sources have compiled lists of languages by their number of speakers. However, all such lists should be used with caution.

• First, it is difficult to define exactly what constitutes a language as opposed to a dialect. For example, Chinese is sometimes considered a single language and sometimes as a language family. Similarly, Hindi is considered sometime a single language or a family including Mewari, Chattisgarhi, Bhojpuri etc., but together with Urdu it also is often considered a single language Hindustani.
• Second, there is no single criterion for how much knowledge is sufficient to be counted as a second-language speaker. For example, English has about 350 million native speakers but, depending on the criterion chosen, can be said to have as many as 2 billion speakers.