🌐 Added i18next

frontend/src/lib/i18n/translation-service.ts

@@ -0,0 +1,59 @@
+import type { I18nService } from './i18n-service';
+import { derived, writable } from 'svelte/store';
+import type { Readable, Writable } from 'svelte/store';
+
+export type TType = (text: string, replacements?: Record<string, unknown>) => string;
+
+export interface TranslationService {
+	locale: Writable<string>;
+	translate: Readable<TType>;
+}
+
+export class I18NextTranslationService implements TranslationService {
+	public locale: Writable<string>;
+	public translate: Readable<TType>;
+
+	constructor(i18n: I18nService) {
+		i18n.initialize();
+		this.locale = this.createLocale(i18n);
+		this.translate = this.createTranslate(i18n);
+	}
+
+	// Locale initialization.
+	// 1. Create a writable store
+	// 2. Create a new set function that changes the i18n locale.
+	// 3. Create a new update function that changes the i18n locale.
+	// 4. Return modified writable.
+	private createLocale(i18n: I18nService) {
+		const { subscribe, set, update } = writable<string>(i18n.i18n.language);
+
+		const setLocale = (newLocale: string) => {
+			i18n.changeLanguage(newLocale);
+			set(newLocale);
+		};
+
+		const updateLocale = (updater: (value: string) => string) => {
+			update((currentValue) => {
+				const nextLocale = updater(currentValue);
+				i18n.changeLanguage(nextLocale);
+				return nextLocale;
+			});
+		};
+
+		return {
+			subscribe,
+			update: updateLocale,
+			set: setLocale
+		};
+	}
+
+	// Create a translate function.
+	// It is derived from the "locale" writable.
+	// This means it will be updated every time the locale changes.
+	private createTranslate(i18n: I18nService) {
+		return derived([this.locale], () => {
+			return (key: string, replacements?: Record<string, unknown>) =>
+				i18n.t(key, replacements);
+		});
+	}
+}