add translation keys (#246)

* Fix i18n tsc issue

"t" can return null by default.
This was already disabled in the config, but it had no effect on tsc.

* Fix translation in "DefaultNavBar"

key was missing and since this is a constant the translation wouldn't update in case the language got changed after first load.

* Enable typing for i18n translation keys

* Add translation keys

src/i18n/translations.ts

@@ -7,12 +7,12 @@
 
 import en from 'i18n/locale/en.json';
 
-const translationHelper = (lng: any) => ({
+const translationHelper = <T>(lng: T) => ({
     translation: lng,
 });
 
 const resources = {
     en: translationHelper(en),
-};
+} as const;
 
 export default resources;