Ask HN: What's the best approach when localizing large scale systems?

I work at a bank in a country where english isn't the first language. As interest has historically been low all our products are only available in our first language.

We're now seeing raised interest from customers who doesn't know our language and we're looking into how we should go about localizing eveything.

Are there any well known strategies or systems for moving a large number repos from scattered strings and messy templates to some kind of localization engine? What should we think about when planning for this?