All about mkv-fomat you can find here For work with multimedia mkv-container it is necessary to download the program mkvtoolnix-unicode-2.0.2-1 (it is possible to download here). After installation start the program mkvmerge GUI ("C:\Program Files\MKVtoolnix\mmg.exe") from the menu "Start"
In the opened window of the program in a folder «Input» press the «add» button, find necessary *.mkv a file on your harddrive and press the "Open" button.
As you see, in the opened container there is one video and one audio tracks.
For example, to add one more audio tracks, it is necessary to press again the «add» button, to find on the harddrive necessary audio a file (preliminary synchronised with your's video) and to press "Open" button
As you see, there was one more audio track. Then it is possible to name it in «Track name:» (on an example, Scarpini) to choose track's language in «Language:» (on an example, Italian) and if you want is chosen that new track played by default at video-file opening, put in «Default track flag» - «yes». Then rename an initial file in «Output name:» is there will be your new video file with two audio tracks.
On it reconfiguration of a new file is finished - it is possible to press «Start muxing».
After the termination of configuration of a new file press "Ok" button and close the program. Then open the created file, on an example, in Widows Media Player Classic (and if at configuration of a new file you have not chosen to play a new track by default) it is chosen the necessary audio track as is shown in a screenshot below (on an example, in the menu Play-> Filters-> ”a file site”-> And: Scarini [Italian])