How many languages are there in the world?

Only one (A biologist looks at human language)...

When we look at the languages of the world, they may seem bewilderingly diverse. From the point of view of communication systems more generally, however, they are remarkably similar to one another. Human language differs from the communicative behavior of every other known organism in a number of fundamental ways, all shared across languages.

By comparison with the communicative devices of herring gulls, honey bees, dolphins or any other non-human animal, language provides us with a system that is not stimulus bound and ranges over an infinity of possible distinct messages. It achieves this with a limited, finite system of units that combine hierarchically and recursively into larger units. The words themselves are structured from a small inventory of sounds basic to the language, individually meaningless elements combined according to a system completely independent of the way words combine into phrases and sentences.

The particular linguistic system that each individual controls goes far beyond the direct experience from which knowledge of it arose. And the principles governing these systems of sounds, words and meanings are largely common across languages, with only limited possibilities for difference (the parameters described above).

In all these ways, human language is so different from any other known system in the natural world that the narrowly constrained ways in which one grammar can differ from another fade into insignificance. For a native of Milan, the differences between the speech of that city and that of Turin may loom large, but for a visitor from Kuala Lumpur both are “Italian.” Similarly, the differences we find across the world in grammars seem very important, but for an outside observer—say, a biologist studying communication among living beings in general—all are relatively minor variations on the single theme of Human language.

As the 11th edition of the Encyclopedia Britannica put it, “[...] all existing human speech is one in the essential characteristics which we have thus far noted or shall hereafter have to consider, even as humanity is one in its distinction from the lower animals; the differences are in nonessentials.” 

Source: linguisticsociety.org

Language vs Dialect

The debate

Faced with the question, linguists like to repeat the grand old observation of the linguist and Yiddishist Max Weinreich, that “a language is a dialect with an army and a navy.”

It’ll be a bit harder to define the difference between language and dialect in the real world.

We think that Portuguese and Spanish are different languages. Then how come a Spanish newspaper readable by a Portuguese speaker?

That is the actual riddle we have been solving for you. These two languages are distinct. But there’s a degree of mutual intelligibility that makes it possible to converse.

Doesn’t it mean to consider Spanish and Portuguese as dialects and not languages? People of Spain and Portugal will object to this.

But this is the truth! Hold on, let me complete the justification.

Spanish and Portuguese are romance languages. It means that both of these are dialects of romance parent languages.

But should we take French, Italian, and Romanian in the same terms?

Mutual intelligibility is a herring in the difference between language and dialect.

English language has different dialects, mutually intelligible and spoken around the globe.

Source: Thelanguagedoctors.org