Q:

How is "instrument" pronounced?

I know how it's pronounced
But yesterday I came across a website for learning English .. and it was good
But in this page 
" 
http://www.learn-english-kids.net/page/6/
"
there is a word which is "instruments" and it is pronounced like there is a "sh" sound .. but I have not ever heard this word prounounced like this way !
is it about dialects or accents? or something else ?

A:

This pronunciation comes about because the speaker is making a conscious and awkward effort to speak very slowly and distinctly. This leads her to ‘overarticulate’—to exaggerate the separation of sounds which in natural speech flow into each other.
The unnatural attempt to distinguish the sounds at the n/s boundary in *instruments' causes her to anticipate the following /t/, because in all three sounds the tip of the tongue is placed at very similar places behind and above the front teeth. The glide is garbled, and /ns/ becomes /ntʃ/, as in inch. 

