remove svelte-i18n dependency, replace with minimalistic implementation

website/src/lib/components/toolbar/tools/Elevation.svelte

@@ -5,7 +5,7 @@
     import { MountainSnow } from 'lucide-svelte';
     import { dbUtils } from '$lib/db';
     import { map } from '$lib/stores';
-    import { _, locale } from 'svelte-i18n';
+    import { _, locale } from '$lib/i18n';
     import { getURLForLanguage } from '$lib/utils';
 
     $: validSelection = $selection.size > 0;