feat: localization (#196)

* Started adding locale translations :)

* Added some more translations

* Working on translating even more pages

* More translations

* Added test default locale retrieval

* replace `intl.formatMessage` with custom `t` hook

* add more translations

* improve title syntax

* add more translations

* translate admin config page

* translated error messages

* add language selecter

* minor fixes

* improve language handling

* add upcoming languages

* add `crowdin.yml`

* run formatter

---------

Co-authored-by: Steve Tautonico <stautonico@gmail.com>

frontend/src/utils/i18n.util.ts

@@ -0,0 +1,42 @@
+import { setCookie } from "cookies-next";
+import { LOCALES } from "../i18n/locales";
+
+const getLocaleByCode = (code: string) => {
+  return Object.values(LOCALES).find((l) => l.code === code) ?? LOCALES.ENGLISH;
+};
+
+// Parse the Accept-Language header and return the first supported language
+const getLanguageFromAcceptHeader = (acceptLanguage?: string) => {
+  if (!acceptLanguage) return "en";
+
+  const languages = acceptLanguage.split(",").map((l) => l.split(";")[0]);
+  const supportedLanguages = Object.values(LOCALES).map((l) => l.code);
+
+  for (const language of languages) {
+    // Try to match the full language code first, then the language code without the region
+    if (supportedLanguages.includes(language)) {
+      return language;
+    } else if (supportedLanguages.includes(language.split("-")[0])) {
+      return language.split("-")[0];
+    }
+  }
+  return "en";
+};
+
+const isLanguageSupported = (code: string) => {
+  return Object.values(LOCALES).some((l) => l.code === code);
+};
+
+const setLanguageCookie = (code: string) => {
+  setCookie("language", code, {
+    sameSite: "lax",
+    expires: new Date(new Date().setFullYear(new Date().getFullYear() + 1)),
+  });
+};
+
+export default {
+  getLocaleByCode,
+  getLanguageFromAcceptHeader,
+  isLanguageSupported,
+  setLanguageCookie,
+};