I like to use Google Sheets for my game localization since it's easy too share a sheet with someone that can do the translating for you, not too hard to access the sheets from within the game itself (or the engine editor) and last but not least you can write Add-Ons for it. I've recently done that and made one that auto-translates your localization sheet. You can get it here.
I have also done a short video on how to use the add-on, if you want to see that first.
If you don't like the set-up you can also have a look at the code on Github and modify it as you see fit.