doc: update lang doc and add chinese locale

doc/languages.md

@@ -2,15 +2,36 @@
 
 Here are the language files for PVP Arena, not (all) created or updated by me.
 
-Download the file and set `lang:` parameter inside the config.yml to 
-value of the second column.
+## How to install a language file
+Download the file and copy it in the folder `plugins/pvparena/`. Then edit the file `config.yml` and 
+set the `language` setting to the new language code (second column below).
+Finally, reload your plugin configuration by running [`/pa reload`](commands/reload.md)
 
-| download                       | lang: value    | language | author          | last update |
-|--------------------------------|----------------|----------|-----------------|-------------|
-| generated                      | 'en' (default) | English  | slipcor/Eredrim | 2025        |
-| [link](../lang/lang_fr.yml)    | 'fr'           | Français | Eredrim         | 2025        |
+| download                       | language code  | language           | author          | last update |
+|--------------------------------|----------------|--------------------|-----------------|-------------|
+| generated                      | 'en' (default) | English            | slipcor/Eredrim | 2025-01     |
+| [link](../lang/lang_fr.yml)    | 'fr'           | Français           | Eredrim         | 2025-01     |
+| [link](../lang/lang_zh-CN.yml) | 'zh-CN'        | Simplified Chinese | Harry_H2O       | 2025-01     |
 
 <br>
 
 > 💡 **Did you know ?**  
-> PVP Arena is powered by community! You can offer your own language file by [creating an issue](https://github.com/Eredrim/pvparena/issues).
+> PVP Arena is powered by community! You can offer your own language file by [creating an issue](https://github.com/Eredrim/pvparena/issues).
+
+## How to create your own language file?
+
+Browse your PVPArena repository (`plugins/pvparena/`) and copy the file named `lang_en.yml` to `lang_<lang_code>.yml`
+where `<lang_code>` is any code to distinguish your language (ideally an 
+[ISO 639-1](https://en.wikipedia.org/wiki/List_of_ISO_639_language_codes) language code, but in reality it doesn't matter).  
+Then you can edit all values of the file. Mind to respect YAML rules (for instance using quotes around the message if 
+you need to write a colon character).
+
+Finally, edit the file `config.yml`, set the `language` setting to the new language code and reload your plugin 
+configuration by running [`/pa reload`](commands/reload.md).
+
+> 🚩 **Tips:**
+> * As soon as your configuration is set to use your own language file, you can edit it and reload it as much as you 
+> want to test it.
+> * You can use color codes and styling codes in language file
+> * Some messages contain argument values, their format is `%<number>%`. You can move them within the message but don't
+> remove them. However, a part of the meaning will be lost.