Ask HN: How does a modern web service handle multiple languages(locales)?

I would like to know how a modern web service handles such at a rather large scale. At the moment, I am working with a web service fully translated in 3+ languages and plans for more.

There are several frameworks all over various web stacks that support multiple locales/languages, either with the internationalization API or something named similarly.

However, at some point this doesn't seem to feel like using the right tool for the job. After talking with my colleagues, I have had some recent ideas about using an isolated web service to handle multiple languages requesting translations over REST.

What do you think are pros and cons of such approach ? And of course, what would be the industry-proven way of handling multiple languages, so that I don't stupidly waste a lot of time and money ?