All known languages require the following features:
1. Sufficient brain space to house the dictionary and grammar.
2. Specific features of the vocal apparatus including the vocal cords, the muscles of the tongue and mouth enabling articulation.
3. An ability to control breathing which allows for long fluent articulate phrases and the ability to modulate intonation subtly over the length of a single breadth.
Our nearest primate relatives (i.e. monkeys and apes) do not have any such control which explains why attempts to train them to speak have been so unsuccessful.
Birds alone can imitate human speech. The birds brain, vocal apparatus, or syrinx (literally, ‘flute’) and their ability to control their breathing explains why.