How does the language option works in multiple language DVD?

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I wonder what is the technology and the logic that stands behind the multiple language DVD movies.

I will be giving some more detailed information:
From the scientific point a view a multimedia file is consisted of the audio and the video signal, my knowledge is limited in this area, but i suppose that these 2 signals should be separated from each other, while the video signal goes on the audio signal should be changed, so we make synchronization when we change the language in the DVD movies, unfortunately I don't know what type of software, technology or tools are used for these purpose.

Any type of help is welcomed, any websites or forums please

Thanks in advance )))