It does not convert the entire application to 64-bit; that is determined by which Office suite you installed (64-bit vs. 32-bit). The language pack must match the bitness of your installed Office.
There are several reasons why you might need to install the English language pack for Office 2016: microsoft office 2016 english language pack 64-bit
Under the menu, look for the dropdown list, choose English , and click Add . It does not convert the entire application to