When your system/computer is set to the language you want to use - You can change the language in SMART the same way you install any other plugin, just find it in the plug-in list, check the box off and press ok (see screenshot)
When you want to run SMART in a different language to your system - You can force SMART to use a particular language by editing the SMART.ini file which is located next to the SMART.exe file (on the windows build). You can add a line to the end of this file that says:
-Duser.language=fr
fr = FRENCH, put in whatever supported language you want. You have to
use the two or three character language code (listed below).
A short video is available here - link
The languages that are supported to varying degrees are:
ar - Arabic
es - Spanish
fr - French
hi - Hindi
in - Indonesian
ka - Georgian
kar - Karen
km - Khmer
lo - Loas
mn - Mongolian
ms - Malay
pt - Portuguese
ru - Russian
sw - Swahili
th - Thai
uk - Ukranian
vi - Vietnamese
zh - Chinese