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/components/util/helpers.ts

@@ -1,19 +0,0 @@
-/*
- * Copyright (C) Contributors to the Suwayomi project
- *
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
-
-// eslint-disable-next-line import/prefer-default-export
-export const pluralize = (count: number, input: string | { one: string; many: string }) => {
-    if (typeof input === 'string') {
-        return `${input}${count === 1 ? '' : 's'}`;
-    }
-    return input[count === 1 ? 'one' : 'many'];
-};
-
-export const interpolate = (count: number, input: { one: string; many: string }) => {
-    const text = count === 1 ? input.one : input.many;
-    return text.replaceAll('%count%', count.toString());
-};