diff --git a/support/doc/plugins/guide.md b/support/doc/plugins/guide.md
index 8f8884d00..1aae65a1c 100644
--- a/support/doc/plugins/guide.md
+++ b/support/doc/plugins/guide.md
@@ -11,6 +11,11 @@
   - [Server helpers (only for plugins)](#server-helpers-only-for-plugins)
     - [Settings](#settings)
     - [Storage](#storage)
+    - [Update video constants](#update-video-constants)
+  - [Client helpers (themes & plugins)](#client-helpers-themes--plugins)
+  - [Plugin static route](#plugin-static-route)
+    - [Translate](#translate)
+    - [Get public settings](#get-public-settings)
   - [Publishing](#publishing)
 - [Write a plugin/theme](#write-a-plugintheme)
   - [Clone the quickstart repository](#clone-the-quickstart-repository)
@@ -18,8 +23,10 @@
   - [Update README](#update-readme)
   - [Update package.json](#update-packagejson)
   - [Write code](#write-code)
+  - [Add translations](#add-translations)
   - [Test your plugin/theme](#test-your-plugintheme)
   - [Publish](#publish)
+- [Plugin & Theme hooks/helpers API](#plugin--theme-hookshelpers-api)
 - [Tips](#tips)
   - [Compatibility with PeerTube](#compatibility-with-peertube)
   - [Spam/moderation plugin](#spammoderation-plugin)
@@ -40,18 +47,6 @@ A plugin registers functions in JavaScript to execute when PeerTube (server and
  For example to replace words in video comments, or change the videos list behaviour
  * `action`: used to do something after a certain trigger. For example to send a hook every time a video is published
  * `static`: same than `action` but PeerTube waits their execution
- 
-Example:
-
-```js
-// This register function is called by PeerTube, and **must** return a promise
-async function register ({ registerHook, registerSetting, settingsManager, storageManager, peertubeHelpers }) {
-  registerHook({
-    target: 'action:application.listening',
-    handler: () => displayHelloWorld()
-  })
-}
-```
 
 On server side, these hooks are registered by the `library` file defined in `package.json`.
 
@@ -63,6 +58,27 @@ On server side, these hooks are registered by the `library` file defined in `pac
 }
 ```
 
+And `main.js` defines a `register` function:
+
+Example:
+
+```js
+async function register ({
+  registerHook,
+  registerSetting,
+  settingsManager,
+  storageManager,
+  videoCategoryManager,
+  videoLicenceManager,
+  videoLanguageManager
+}) {
+  registerHook({
+    target: 'action:application.listening',
+    handler: () => displayHelloWorld()
+  })
+}
+```
+
 
 On client side, these hooks are registered by the `clientScripts` files defined in `package.json`.
 All client scripts have scopes so PeerTube client only loads scripts it needs:
@@ -84,6 +100,17 @@ All client scripts have scopes so PeerTube client only loads scripts it needs:
 }
 ```
 
+And these scripts also define a `register` function:
+
+```js
+function register ({ registerHook, peertubeHelpers }) {
+  registerHook({
+    target: 'action:application.init',
+    handler: () => onApplicationInit(peertubeHelpers)
+  })
+}
+```
+
 ### Static files
 
 Plugins can declare static directories that PeerTube will serve (images for example) 
@@ -93,6 +120,17 @@ or `/themes/{theme-name}/{theme-version}/static/` routes.
 ### CSS
 
 Plugins can declare CSS files that PeerTube will automatically inject in the client.
+If you need to override existing style, you can use the `#custom-css` selector:
+
+```
+body#custom-css {
+  color: red;
+}
+
+#custom-css .header {
+  background-color: red;
+}
+```
 
 ### Server helpers (only for plugins)
 
@@ -124,6 +162,58 @@ const value = await storageManager.getData('mykey')
 await storageManager.storeData('mykey', { subkey: 'value' })
 ```
 
+#### Update video constants
+
+You can add/delete video categories, licences or languages using the appropriate managers:
+
+```js
+videoLanguageManager.addLanguage('al_bhed', 'Al Bhed')
+videoLanguageManager.deleteLanguage('fr')
+
+videoCategoryManager.addCategory(42, 'Best category')
+videoCategoryManager.deleteCategory(1) // Music
+
+videoLicenceManager.addLicence(42, 'Best licence')
+videoLicenceManager.deleteLicence(7) // Public domain
+```
+
+### Client helpers (themes & plugins)
+
+### Plugin static route
+
+To get your plugin static route:
+
+```js
+const baseStaticUrl = peertubeHelpers.getBaseStaticRoute()
+const imageUrl = baseStaticUrl + '/images/chocobo.png'
+```
+
+#### Translate
+
+You can translate some strings of your plugin (PeerTube will use your `translations` object of your `package.json` file):
+
+```js
+peertubeHelpers.translate('User name')
+   .then(translation => console.log('Translated User name by ' + translation))
+```
+
+#### Get public settings
+
+To get your public plugin settings:
+
+```js
+peertubeHelpers.getSettings()
+  .then(s => {
+    if (!s || !s['site-id'] || !s['url']) {
+      console.error('Matomo settings are not set.')
+      return
+    }
+    
+    // ...
+  })
+``` 
+
+
 ### Publishing
 
 PeerTube plugins and themes should be published on [NPM](https://www.npmjs.com/) so that PeerTube indexes
@@ -215,6 +305,24 @@ Now you can register hooks or settings, write CSS and add static directories to
 and will be supported by web browsers.
 If you want to write modern JavaScript, please use a transpiler like [Babel](https://babeljs.io/).
 
+### Add translations
+
+If you want to translate strings of your plugin (like labels of your registered settings), create a file and add it to `package.json`:
+
+```json
+{
+  ...,
+  "translations": {
+    "fr-FR": "./languages/fr.json",
+    "pt-BR": "./languages/pt-BR.json"
+  },
+  ...
+}
+```
+
+The key should be one of the locales defined in [i18n.ts](https://github.com/Chocobozzz/PeerTube/blob/develop/shared/models/i18n/i18n.ts).
+You **must** use the complete locales (`fr-FR` instead of `fr`).
+
 ### Test your plugin/theme
 
 You'll need to have a local PeerTube instance: