Taken from dictionary for easy reference: 

(إن شاء الله) is an Arabic
term evoked by Arabic, Farsi, and Urdu speakers to indicate hope for an
aforementioned event to occur in the future. The Turks render it
"İnşallah". The phrase translates into English as "God willing" or "If it is God's will".

.....

First of all this does not apply on ME only, this is used around the globe wherever Mulsims are living. 

We use Inshah'Allah to seek Allah's help (also Alhamdulilah, Subhan'Allah, Mash'Allah are very common) these words are repeated by every muslim at least once in his daily life ....  it is also called Tasbih (تسبيح) is a form of dhikr that involves the repetitive utterances of short sentences glorifying God. The term can also be used loosely to refer to any kind of dhikr.

 

Therefore, when your subordinate said Inshah'Allah and later the turn back with negative response that he doesn't know how to use Excel, now here one more thing that he might know basic excel but not at the advanced level, therefore he said Inshah'Allah (to give a try with the help of God).

 

Sorry, I should say your company has a poor recruitment system. 

 

But here, I agree with you that in the 1st step he should have seek your help on how prepare a spreadsheet in Excel, since this has something to do with the deadline.
 

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