To begin with, a characteristic that is shared by all languages is that they are arbitrary, which is in its most elemental form is demonstrated in the absence of a natural relationship between the codes of the common language and the events or properties they refer to, between form and meaning. We associate specific concepts to specific words as a result of our process of enculturation.
A second shared characteristic is the use of discrete elements, or elements that are contrasting and do not form a continuum (always the same sound). If we change the phoneme of a word, the result will be a word that does not exist and lacks meaning or a word with an entirely different meaning.
Thirdly, there is the double organization of the structure of languages, which are made up of a smaller number of arbitrary sounds that lack meaning. The speakers perceive them as different and, as a result of the combination of these sounds in chains of meaning (a word may have different meanings according to context; phonemes can also change their location).
Lastly, this duality allows for an unlimited semantic productivity, which means that given a finite number of units, we can generate an infinite number of messages.