It started with human spreaded all around the world.

They created and started to communicate in their own language.

In their own language, due to the different clan and region, the language has variant -  i.e. dialect.

Then, they want to communicate with other races.

They adopted 'lingua franca' (e.g. English)

They still use their own language to communicate.

But the usage of their dialects become lesser and lesser (for example, in my generation, not many of my family knows Hakka)

First, they forget about the dialects.

Then finally they stick to lingua franca (because it's something that everybody would understand), and eventually forget about their own language (if you have a simpler choice, why not?)

Next, they develop machine/gadget that do not need human to speak - it uses psychic power to communicate - something like ant, but no touching needed - which is easier and faster to understand what other people want.

One day, something bad happened, the machine/gadget are all destroyed.

Human has forgotten how to speak.

So, if you wanna know what will happen next, you start again from the top.