A family of Microsoft word processing software products for creating web, email, and print documents.
Please note the following: there's a difference between paragraph direction and text alignment. You're trying to change the text alignment to the left, but this won't solve the problem. The solution is to make the paragraph left-to-right (LTR), but unfortunately you don't have this option because your Word doesn't support Arabic. Those who have Arabic-enabled Word can choose RTL paragraph direction in order to type Arabic, and LTR paragraph direction to type English.
Here's a workaround for your situation (based on Word 2010):
Click File > Options.
When the Word Options window opens, go to Quick Access Toolbar.
Under Choose commands from, choose All Commands.
Scroll down to Left-to-Right Text Direction, double click it to add it to the column to the right.
Click OK.
You'll notice that the Quick Access Toolbar has now a new button.
Now, when you insert a comment that turns to be RTL, click that button and it will make your comment LTR.