Internationalization + Finnish language (#181)

* I18n with next-intl

* package-lock

* Finnish translations

* Development fix

* Use locale for positioning currency symbol

* Translations: Expenses.ActiveUserModal

* Translations: group 404

* Better translation for ExpenseCard

* Apply translations in CategorySelect search

* Fix for Finnish translation

* Translations for ExpenseDocumentsInput

* Translations for CreateFromReceipt

* Fix for Finnish translation

* Translations for schema errors

* Fix for Finnish translation

* Fixes for Finnish translations

* Prettier

---------

Co-authored-by: Sebastien Castiel <sebastien@castiel.me>

src/lib/locale.ts

@@ -0,0 +1,42 @@
+'use server'
+
+import { Locale, Locales, defaultLocale, locales } from '@/i18n'
+import { match } from '@formatjs/intl-localematcher'
+import Negotiator from 'negotiator'
+import { cookies, headers } from 'next/headers'
+
+const COOKIE_NAME = 'NEXT_LOCALE'
+
+function getAcceptLanguageLocale(requestHeaders: Headers, locales: Locales) {
+  let locale
+  const languages = new Negotiator({
+    headers: {
+      'accept-language': requestHeaders.get('accept-language') || undefined,
+    },
+  }).languages()
+  try {
+    locale = match(languages, locales, defaultLocale)
+  } catch (e) {
+    // invalid language
+  }
+  return locale
+}
+
+export async function getUserLocale() {
+  let locale
+
+  // Prio 1: use existing cookie
+  locale = cookies().get(COOKIE_NAME)?.value
+
+  // Prio 2: use `accept-language` header
+  // Prio 3: use default locale
+  if (!locale) {
+    locale = getAcceptLanguageLocale(headers(), locales)
+  }
+
+  return locale
+}
+
+export async function setUserLocale(locale: Locale) {
+  cookies().set(COOKIE_NAME, locale)
+}