Using a dictionary library for i18n, also shows how to use i18n with navigation plugin.

.eleventy.js

@@ -1,9 +1,11 @@
 const { DateTime } = require("luxon");
+const rosetta = require("rosetta");
 const markdownItAnchor = require("markdown-it-anchor");
 const pluginRss = require("@11ty/eleventy-plugin-rss");
 const pluginSyntaxHighlight = require("@11ty/eleventy-plugin-syntaxhighlight");
 const pluginNavigation = require("@11ty/eleventy-navigation");
 const { EleventyI18nPlugin } = require("@11ty/eleventy");
+const languageStrings = require("./i18n.js");
 
 module.exports = function(eleventyConfig) {
   eleventyConfig.ignores.add("README.md");
@@ -78,6 +80,19 @@ module.exports = function(eleventyConfig) {
     showVersion: true,
   });
 
+  // i18n filter using Rosetta
+  const rosettaLib = rosetta(languageStrings);
+
+  eleventyConfig.addFilter("i18n", function (key, lang) {
+    const I18N_PREFIX = "i18n.";
+    if(key.startsWith(I18N_PREFIX)) {
+      key = key.slice(I18N_PREFIX.length);
+    }
+    // depends on page.lang in 2.0.0-canary.14+
+    let page = this.page || this.ctx?.page || this.context?.environments?.page || {};
+    return rosettaLib.t(key, {}, lang || page.lang);
+  });
+
   return {
     // Control which files Eleventy will process
     // e.g.: *.md, *.njk, *.html, *.liquid