How editor plugins use this feature:
1. Pick a unique translation domain name.
2. `_enter_tree()`: load translations into that translation domain.
3. Call `set_translation_domain()` for its root UI node.
4. `_exit_tree()`: remove that translation domain.
Plugins can also set the translation domain to `godot.editor` for
nested nodes that should use editor translations. `EditorFileDialog`
automatically does this.
Haoyu Qiu