Create a shortcut of Grip.exe (in the base directory) or Grip-Win64-Shipping.exe (located in GRIP\Grip\Binaries\Win64), go into the shortcut's properties, and add the parameter

-culture="xx_YY"

at the end of the target's path (including a blank after .exe/before -culture...).

Replace xx_YY with one of the following:

en_GB
de_DE (German)
es_ES (Spanish
fr_FR (French)
it_IT (Italian)
ja_JP (Japanese)
ko_KR (Korean)
pl_PL (Polish)
ru_RU (Russian)
zh_CN (Chinese)

for the desired language.

Apply, close properties, start from the shortcut, and voilà, the game should "speak" the language it has been set to via the parameter.