What is the most complex language?

If artificial languages are being counted, then definitely Ithkuil.

It has the nomination of being the most complex language ever conceived.

The phonological system includes 65 consonants and 17 vowels, along with 3600 roots that can be modified with extremely complex grammatical rules by a huge number of affixes, prefixes, suffixes, infixes and interfixes.

The grammar alone takes up numerous pages, and no one in the world, not even the creator of the language is even remotely able to speak it fluently.

It is in fact designed to condense large amounts of linguistic information using as few words as possible. Most expressions appear much shorter when translated into Ithkuil.

To make a point, the 54 characters above translate into English as ‘As our vehicle leaves the ground and plummets over the edge of the cliff towards the bottom of the valley, I wonder if it could be declared that I am guilty of an act of moral failure, having failed to maintain a correct course along the roadway’.

Some have postulated a connection between the characteristics of languages and the cognitive abilities of the people who speak them (the Sapir-Whorf hypothesis).

Along these lines, Stanislav Kozlovsky hypothesizes that a native speaker of Ithkuil can think more than five or six times faster than a speaker of a typical natural language.