client: Set fallback value for LocalizationContext

Reduces the number of errors reported by TypeScript compiler in strict mode from 398 to 294.

Author: jtojnar

client/js/helpers/i18n.ts

@@ -116,7 +116,9 @@ export function i18nFormat(
     return formatted;
 }
 
-export const LocalizationContext = React.createContext(undefined);
+export const LocalizationContext = React.createContext<Translate>(() => {
+    throw new Error('Missing l10n context');
+});
 
 export type Translate = (
     translated: MessageKey,