How to change locale and make it stay that way?

My friend has a LG V10 and unfortunately, it doesn't have the language he wants (Hebrew) as part of the stock ROM. I've googled around and found that there are apps that enable you to change locale to more languages than the ones that are included with the ROM. I've used one (MoreLocale2), and it works. The issue is that the language is reverted back to default (English) after the device is rebooted ;/ After seeing that I tried using other apps that work the same way, but they all seem to have the same issue. Is there any way to change locale and force it to stay that way after a reboot ? ;/ I'm not really interested in changing ROMs, this isn't my device and I'm looking for a simple solution as I'm doing this as a favor. Thanks!