Defining Translations

The first part of setting up i18n in Perseus is to state that your app uses it, which is done in PerseusApp like so (taken from the i18n example):

mod error_pages;
mod templates;

use perseus::{Html, PerseusApp};

#[perseus::main]
pub fn main<G: Html>() -> PerseusApp<G> {
    PerseusApp::new()
        .template(crate::templates::index::get_template)
        .template(crate::templates::about::get_template)
        .template(crate::templates::post::get_template)
        .error_pages(crate::error_pages::get_error_pages)
        .locales_and_translations_manager("en-US", &["fr-FR", "es-ES"])
}

There are two parameters to the .locales() function: the default locale for your app, and then any other locales it supports (other than the default). Each of these locales should be specified in the form xx-XX, where xx is the language code (e.g. en for English, fr for French, la for Latin) and XX is the region code (e.g. US for United States, GB for Great Britain, CN for China).

Routing

After you've enabled i18n like so, every page on your app will be rendered behind a locale. For example, /about will become /en-US/about, /fr-FR/about, and/es-ES/about in the above example. These are automatically rendered by Perseus at build-time, and they behave exactly the same as every other feature of Perseus.

Of course, it's hardly optimal to direct users to a pre-translated page if they may prefer it in another language, which is why Perseus supports locale detection automatically. In other words, you can direct users to /about, and they'll automatically be redirected to /<locale>/about, where <locale> is their preferred locale according to navigator.languages. This matching is done based on RFC 4647, which defines how locale detection should be done.

Adding Translations

After you've added those definitions to PerseusApp, if you try to run your app, you'll find that ever page throws an error because it can't find any of the translations files. These must be defined under translations/ (which should be NEXT to /src, not in it!), though this can be customized (explained later). They must also adhere to the naming format xx-XX.ftl (e.g. en-US.ftl). .ftl is the file extension that Fluent files use, which is the default translations system of Perseus. If you'd like to use a different system, this will be explained later.

Here's an example of a translations file (taken from here):

hello = Hello, { $user }!
about = Welcome to the about page (English)!

You can read more about Fluent's syntax here (it's very powerful).