Merged in feature/refactor-lang (pull request #387)

feat: SW-238 Avoid prop drilling of lang

Approved-by: Michael Zetterberg

i18n/i18n.md

@@ -0,0 +1,17 @@
+# Internationalization
+
+## The `lang` route parameter
+
+All page paths starts with a language parameter, e.g. `/sv/utforska-scandic/wi-fi`.
+
+### Get the language in a client component
+
+We have a hook called `useLang` that directly returns the `lang` parameter from the path.
+
+### Get the language in a server component
+
+In order to not prop drill that all the way from a page we use React's `cache` in a way that resembles React`s context, but on the server side.
+
+For this to work we must set the language with `setLang` on all root layouts and pages, including pages in parallel routes. Then we can use `getLang` in the components where we need the language.
+
+This was inspired by [server-only-context](https://github.com/manvalls/server-only-context)

i18n/serverContext.ts

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+import { cache } from "react"
+
+import { Lang } from "@/constants/languages"
+
+const getRef = cache(() => ({ current: Lang.en }))
+
+/**
+ * Set the language for the current request
+ *
+ * It works kind of like React's context,
+ * but on the server side, per request.
+ *
+ * @param newLang
+ */
+export const setLang = (newLang: Lang) => {
+  getRef().current = newLang
+}
+
+/**
+ * Get the global language set for the current request
+ */
+export const getLang = () => getRef().current