fix: 'Untitled' is not translated

closes #5949

app/models/Document.ts

@@ -1,5 +1,5 @@
 import { addDays, differenceInDays } from "date-fns";
-import { t } from "i18next";
+import i18n, { t } from "i18next";
 import floor from "lodash/floor";
 import { action, autorun, computed, observable, set } from "mobx";
 import { ExportContentType } from "@shared/types";
@@ -241,11 +241,6 @@ export default class Document extends ParanoidModel {
     return this.title === "";
   }
 
-  @computed
-  get titleWithDefault(): string {
-    return this.title || "Untitled";
-  }
-
   @computed
   get permanentlyDeletedAt(): string | undefined {
     if (!this.deletedAt) {
@@ -279,6 +274,10 @@ export default class Document extends ParanoidModel {
     return floor((this.tasks.completed / this.tasks.total) * 100);
   }
 
+  get titleWithDefault(): string {
+    return this.title || i18n.t("Untitled");
+  }
+
   @action
   updateTasks(total: number, completed: number) {
     if (total !== this.tasks.total || completed !== this.tasks.completed) {