Human languages ranked by their number of native speakers are as follows. All such rankings should be used with caution, because it is not possible to devise a coherent set of linguistic criteria for distinguishing languages in a dialect continuum.^[1] For example, a language is often defined as a set of mutually intelligible varieties, but independent national standard languages may be considered separate languages even though they are largely mutually intelligible, as in the case of Danish and Norwegian.^[2] Conversely, many commonly accepted languages, including German, Italian and even English encompass varieties that are not mutually intelligible.^[1] While Arabic is sometimes considered a single language centred on Modern Standard Arabic, other authors consider its mutually unintelligible varieties separate languages.^[3] Similarly, Chinese is sometimes viewed as a single language because of a shared culture and common literary language.^[4] It is also common to describe various Chinese dialect groups, such as Mandarin, Wu and Yue, as languages, even though each of these groups contains many mutually unintelligible varieties.^[5]

There are also difficulties in obtaining reliable counts of speakers, which vary over time because of population change and language shift. In some areas, there is no reliable census data, the data is not current, or the census may not record languages spoken, or record them ambiguously. Sometimes speaker populations are exaggerated for political reasons, or speakers of minority languages may be underreported in favour of a national language.^[6]