[PLEASE HELP] How to edit a GFX file?

I want to edit file 'S4_62ECC59A_00000000_5C7CB2846F0FCA7A %% + _ GFX.gfx' to add Vietnamese language. A modder has edited this file to add Vietnamese fonts to the game (no more error boxes) but currently that file (http://www.simfileshare.net/download/1916752/) is outdated because the game accesses. Updated continuously.

Let me ask if I want to edit, what software should I use to do it: <

Hope you can guide me in detail because these lines I translate from Google Translate.