add ttag + next usage example

docs/next-js.md

@@ -0,0 +1,144 @@
+---
+id: next-js
+title: Next
+---
+
+At the end of this short tutorial you will learn how to set up the localization
+process for [Next JS](https://nextjs.org/) and the ttag library.
+
+## Step 1. Installation
+
+Install ttag dependencies in your Next project.
+
+```bash
+npm i ttag
+npm i -D ttag-cli
+```
+
+## Step 2. Create .po file for translations
+
+At this step, we should create `.po` file for the language that we want to translate to.
+For this example, we will create `.po` file with all appropriate settings for the Ukrainian language (`uk` code).
+
+```bash
+mkdir i18n # create a separate dir to keep translation files
+npx ttag init uk i18n/uk.po
+```
+
+> You can find the list of all available language codes here - https://www.w3.org/International/O-charset-lang.html
+
+## Step 3. Wrap strings with tags
+
+Let's edit `src/pages/index.tsx` and wrap the **"Home page"** string to practice translating a single string:
+
+```tsx
+export default function Home() {
+  return <div>{t`Home page`}</div>;
+}
+```
+
+## Step 4. Update the translation file and add a translation
+
+In this step, we will use `update` command from `ttag-cli` to extract translations from the sources.
+This will also update references to the translated string and remove strings that aren't present in the source files.
+
+```bash
+npx ttag update i18n/uk.po src/
+```
+
+After this, we should see that the new translation was added to the `i18n/uk.po` file:
+
+```po
+#: src/pages/index.tsx:4
+msgid "Home page"
+msgstr ""
+```
+
+Let's add a translation:
+
+```po
+#: src/pages/index.tsx:4
+msgid "Home page"
+msgstr "Домашня сторінка"
+```
+
+## Step 5. Let's parse .po file to json
+
+It's necessary for easier import and use
+
+```bash
+npx ttag po2json i18n/uk.po > i18n/uk.po.json
+```
+
+
+## Step 6. Add translation to our App
+
+You should add file `_app.jsx` to pages folder if you haven't and edit it in the next way:
+
+```tsx
+// /src/pages/_app.tsx
+import type { AppProps } from "next/app";
+import { addLocale } from "ttag";
+import translationUk from "../../i18n/uk.po.json";
+
+addLocale("uk", translationUk);
+
+export default function MyApp({ Component, pageProps }: AppProps) {
+  return (
+    <>
+      <Component {...pageProps} />
+    </>
+  );
+}
+```
+
+
+## Step 7. Internationalization in Next config
+> You can find more information on this topic in [Next Docs](https://nextjs.org/docs/pages/building-your-application/routing/internationalization)
+
+Next js has locale strategies with subpath `example.com/uk/blog` and domain `example.uk/blog`. 
+In our example we will implement first variant, we should edit file `next.config.js` and add in config object `i18n` field with next params
+
+```js
+const nextConfig = {
+  ...
+  i18n: {
+    locales: ["en-US", "uk"],
+    defaultLocale: "en-US",
+  },
+  ...
+};
+
+module.exports = nextConfig;
+
+```
+After this configuration we will get our locale when we will use Next hook `useRouter`
+
+
+## Step 7. Use necessary locale 
+
+We need return to file `src/pages/_app.jsx` and add next changes
+
+```jsx
+// /src/pages/_app.tsx
+
+import type { AppProps } from "next/app";
+import { addLocale, useLocale } from "ttag";
+import { useRouter } from "next/router";
+import translationUk from "../../i18n/uk.po.json";
+
+addLocale("uk", translationUk);
+
+export default function MyApp({ Component, pageProps }: AppProps) {
+  const router = useRouter();
+
+  useLocale(router.locale);
+
+  return (
+    <>
+      <Component {...pageProps} />
+    </>
+  );
+}
+```
+You can see full demo in https://github.com/ttag-org/ttag-next-example

website/i18n/en.json

@@ -38,6 +38,9 @@
       "multiline-strings": {
         "title": "Multiline strings"
       },
+      "next-js": {
+        "title": "Next"
+      },
       "ngettext": {
         "title": "ngettext (plurals)"
       },

website/sidebars.json

@@ -6,7 +6,8 @@
       "webpack",
       "typescript",
       "create-react-app",
-      "gatsby"
+      "gatsby",
+      "next-js"
     ],
     "Tags and Functions": [
       "tag-gettext",