Pixelorama now requires at least Godot 3.1.2 or 3.2.x to work, because TranslationServer.get_loaded_locales() was not included in older versions. If you're using an older version of Godot, please update. Godot 3.2.1 is the currently recommended version, until 3.2.2 is out.
Also updated the list of the translators.