1. The original Japanese version of the game is already installed, so if you need a Japanese version, just launch Launcher from the folder "Steins; Gate 0 / Game" and enjoy the game.
2. If you want an English version of the game, put the files from the “Steins; Gate 0 / English Patch (rev8) by RikuKH3 / SG0_pc_engpatch_rev8_byRikuKH3” folder to the folder “Steins; Gate 0 / Game” with replace. .
3. Find the file bg.mpk in the game folder "Steins; Gate 0 / Game / USRDIR", open its 'Properties' and make sure that the 'Read only' checkbox is unchecked in the 'Attributes', then move it to the folder “Steins;Gate 0/English Patch (rev8) by RikuKH3/SG0_pc_bg_rev1_byRikuKH3” from the downloaded archive with the patch. Then run sg0_bg_en.bat, then transfer the patched bg.mpk back to the game folder “Steins; Gate 0 / Game / USRDIR”.