Added spanish i18n (#73)

Tests will be fixed right after.

Author: GoOz

css/app.css

@@ -440,6 +440,9 @@ input[type="file"]:is(:hover, :focus, :active)::file-selector-button {
 .tab.pl::after {
   content: "🇵🇱";
 }
+.tab.es::after {
+  content: "🇪🇸";
+}
 
 .tab-panel {
   border-top: 1px solid var(--grey);

eleventy.config.js

@@ -25,11 +25,12 @@ export default async function (eleventyConfig) {
     fallbackLocales: {
       en: "fr",
       ru: "en",
-      pl: "pl"
+      pl: "pl",
+      es: "es"
     },
   });
   eleventyConfig.addPlugin(geti18nCollection, {
-    locale: ["en", "fr", "ru", "pl"],
+    locale: ["en", "fr", "ru", "pl", "es"],
   });
 
   eleventyConfig.addPassthroughCopy("img");