fix: switching languages when writing a post clears all content (#556)

* Fix 552: check if language changes before invalidating

* Fix 551: by subscribing to onSetLanguageTag

src/routes/LanguageSwitcher.svelte

@@ -1,19 +1,21 @@
 <script lang="ts">
-  import { languageTag } from "$paraglide/runtime";
+  import { languageTag, onSetLanguageTag } from "$paraglide/runtime";
   import { page } from "$app/stores";
   import { i18n } from "$lib/utils/i18n";
   import { invalidateAll } from "$app/navigation";
   import { twMerge } from "tailwind-merge";
 
   let clazz = "";
   export { clazz as class };
+  onSetLanguageTag(() => {
+    invalidateAll();
+  });
 </script>
 
 <a
   class={twMerge("btn btn-ghost", clazz)}
   href={i18n.route($page.url.pathname)}
   hreflang={languageTag() === "sv" ? "en" : "sv"}
-  on:click={() => invalidateAll()}
 >
   <slot>
     {languageTag() === "sv" ? "EN" : "SV"}