Add localization documentation

A bit of info about working with the translations.

addons/block_code/README.md

@@ -66,6 +66,43 @@ Lean into animations! Godot's animations functionality goes beyond just simple a
 
 Please share feedback in the [Godot Forum Block Coding thread](https://forum.godotengine.org/t/block-coding-high-level-block-based-visual-programming/68941).
 
+## Localization
+
+The plugin supports translations through Godot's [gettext][godot-gettext]
+support. We welcome contributions to make the plugin work better in your
+language! However, please note that translations in the Godot editor **will
+only work with Godot 4.4 or newer**.
+
+The gettext PO files are located in the `addons/block_code/locale` directory.
+See the Godot [documentation][godot-gettext] for instructions on working with
+PO files.
+
+[godot-gettext]: https://docs.godotengine.org/en/stable/tutorials/i18n/localization_using_gettext.html
+
+For developers, a few things need to be done to keep the translatable strings
+up to date.
+
+* If files are added or removed, the list of translatable files needs to be
+  updated. This can be done by using the **Add** dialog in the [POT
+  Generation][pot-generation] tab. Or you can use the **Project → Tools →
+  Update BlockCode translated files** menu item in the editor.
+
+* If translatable strings have changed, the POT file needs to be updated. This
+  can be done by using the **Generate POT** dialog in the [POT
+  Generation][pot-generation] tab. Or you can use the **Project → Tools →
+  Regenerate BlockCode POT file** menu item in the editor.
+
+* If the POT file has changed, the PO message files need to be updated. This
+  can be done using the gettext `msgmerge` tool in the
+  `addons/block_code/locale` directory:
+  ```
+  for po in *.po; do
+    msgmerge --update --backup=none "$po" godot_block_coding.pot
+  done
+  ```
+
+[pot-generation]: https://docs.godotengine.org/en/stable/tutorials/i18n/localization_using_gettext.html#automatic-generation-using-the-editor
+
 ## Development
 
 ### pre-commit