Translating is a valued contribution
The translations for the software developed by the Linux Mint developers are done using Launchpad. For Khmer that is here (just those 19 applications):
https://translations.launchpad.net/linu ... a/+lang/km. As it states there, there currently is no Khmer translation team for the Linux Mint software (though you can see a few translations have been done). A prospective translator would sign up for a Launchpad account and in this case get in email contact with Clement Lefebvre [root at linuxmint dot com], Linux Mint's project leader, for starting a Linux Mint Khmer translation team.
Linux Mint Main Edition is based on Ubuntu. So except for those 19 applications listed in above link, translations are handled by Ubuntu's Khmer localization team:
https://launchpad.net/~ubuntu-l10n-km. I think the most urgent for translation to Khmer are then those 19 Linux Mint applications, as for the other applications already a translation team is in place from Ubuntu.
I'm a member of the Linux Mint Dutch translation team, so I've seen it in action. Launchpad automates a lot of the translating work. For example, common phrases that are already translated in other applications are put forth as suggestions while you are translating. Even if you just have a Launchpad account, you can already enter translations as a suggestion, which the Linux Mint Khmer translation team can than later accept (for now Clement accepts translations, until such a team is set up).
I would suggest you sign up for a Launchpad account, to get an idea from following the above links. BTW not to diminish the strive for a perfect translation, but to any user not understanding English, having access to a Khmer localized installation makes all the difference regardless of how perfect the translation is

Please share if we can help you further, and thank you for considering doing this!