Userscript - Japanese prompts for WaniKani

// ==UserScript==
// @name        WaniKani Japanese Review Questions
// @namespace   WK_CustomQuestion
// @description Changes the text of the Review or Lesson Quiz question. Original created by hoovard, with extra thanks going to previous authors Rui Pinheiro (LordGravewish) and Ethan. Rewritten by FrostKiwi for the new WaniKani version with OnYomi vs KunYomi detection provided by HaraldN
// @author    FrostKiwi
// @match     *://www.wanikani.com/subjects/review*
// @match     *://www.wanikani.com/recent-mistakes*
// @match     *://www.wanikani.com/subject-lessons*
// @match     *://www.wanikani.com/subjects/extra_study*
// @version     0.5.1
// @license     Do what you want with it (Preferably improve it).
// @grant       none
// ==/UserScript==
// Version 0.5.0 applies to Reviews, Lesson Quizzes and extra studies

(function () {
	const translations = {
		'vocabulary': '単語の',
		'radical': '部首の',
		'kanji': '漢字の',
		'reading': '読み',
		'onyomi': '音読み',
		'kunyomi': '訓読み',
		'meaning': '意味',
		'name': '名'
	};

	let reading_type = null;
	let container = null;
	let categorySpan = null;
	let typeSpan = null;

	/* Predefine the observers to ensure we don't accidentally create more than
	   two in some unknown edge case */
	const observerType = new MutationObserver(() => replaceText(typeSpan));
	const observerCategory = new MutationObserver(() => replaceText(categorySpan));

	function initElements() {
		container = document.querySelector('.quiz-input__question-type-container');
		categorySpan = document.querySelector('.quiz-input__question-category');
		typeSpan = document.querySelector('.quiz-input__question-type');
		observerType.observe(categorySpan, { childList: true });
		observerCategory.observe(typeSpan, { childList: true });
	}

	function replaceText(element) {
		const text = element.innerText.toLowerCase();
		if (translations[text]) {
			element.innerText = translations[text];
			if (reading_type && text == 'reading') {
				element.innerText = translations[reading_type];
			}
		}
	}

	function clearWhitespace() {
		Array.from(container.childNodes).forEach(node => {
			if (node.nodeType === Node.TEXT_NODE && !node.textContent.trim()) {
				container.removeChild(node);
			}
		});
	}

	/* The detection of OnYomi vs KunYomi is provided by HaraldN in his
	   Userscript "WaniKani Katakana For On’yomi" */
	const newQuestion = function (e) {
		if (e.detail.subject.type == 'Kanji' && e.detail.questionType == "reading") {
			reading_type = e.detail.subject.primary_reading_type;
		} else {
			reading_type = null;
		}
		if (!container || !categorySpan || !typeSpan) {
			initElements();
		}
		clearWhitespace();
	}

	window.addEventListener('willShowNextQuestion', newQuestion);
})();