docs: Add multi-language extension information

Author: LightDestory

Docs/Adding.md

@@ -10,6 +10,7 @@ It contains snippets and shortcuts to make developing for AzerothCoreAdmin easie
 I want to add:
 
 1. [Adding a new command button](#Adding-a-new-command-button)
+2. [Adding a new language](#Adding-a-new-language)
 
 ### Adding a new command button
 
@@ -19,3 +20,21 @@ In order to add a button with a command, four steps are required (in toc order):
 2. Write the function in ./Commands/Commands_xxxx.lua
 3. Prototype/init the button, function, text, and tooltip in FunctionInit.lua
 4. Draw the button in the ./Frames/MangFrames_Sectionxxxx.lua
+
+### Adding a new language
+
+**So far, the add-on supports only enUS. To add multi-language support, which was present on the TrinityAdmin v2, it is necessary to retrieve and adapt the code of that version. My adaption aim to a fast release, so I am not going to adapt that feature for now. Any contribution is appreciated.**
+
+The add-on uses two files containing strings:
+
+1. %Your-Language%.lua, which contains the actual text that will be displayed in-game
+2. strings.lua, which contains a set of patterns that will be used by the add-on to retrieve information. There patterns must match with the language that the servers uses to print system messages!
+
+In order to add a language support, three steps are required (in toc order):
+
+1. Translate tooltips and button text into your desired language in a file located in ./Locales/xxxx.lua
+2. Inside ./Locales/strings.lua create a function that will return the internal-usage translated strings
+3. Inside AzerothCoreAdmin look up for the language registration section and add the following:
+
+        Locale:RegisterTranslations("%Your-Language%", function() return Return_%Your-Language%() end)
+        Strings:RegisterTranslations("%Your-Language%", function() return ReturnStrings_%Your-Language%() end)