From 9e1e300c721747db7f8070e949ddb574057fbfca Mon Sep 17 00:00:00 2001
From: Elian Doran <contact@eliandoran.me>
Date: Tue, 21 Oct 2025 16:59:13 +0300
Subject: [PATCH] fix(client): normalize locale when formatting time (closes
 #7444)

---
 apps/client/src/utils/formatters.spec.ts | 10 ++++++++--
 apps/client/src/utils/formatters.ts      | 11 ++++++++++-
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/apps/client/src/utils/formatters.spec.ts b/apps/client/src/utils/formatters.spec.ts
index 4c2f043bc..821207d9f 100644
--- a/apps/client/src/utils/formatters.spec.ts
+++ b/apps/client/src/utils/formatters.spec.ts
@@ -1,8 +1,8 @@
 import { describe, expect, it } from "vitest";
 import options from "../services/options";
-import { formatDateTime } from "./formatters";
+import { formatDateTime, normalizeLocale } from "./formatters";
 
-describe("formatDateTime", () => {
+describe("formatters", () => {
     it("tolerates incorrect locale", () => {
         options.set("formattingLocale", "cn_TW");
 
@@ -10,4 +10,10 @@ describe("formatDateTime", () => {
         expect(formatDateTime(new Date(), "full", "none")).toBeTruthy();
         expect(formatDateTime(new Date(), "none", "full")).toBeTruthy();
     });
+
+    it("normalizes locale", () => {
+        expect(normalizeLocale("zh_CN")).toBe("zh-CN");
+        expect(normalizeLocale("cn")).toBe("zh-CN");
+        expect(normalizeLocale("tw")).toBe("zh-TW");
+    });
 });
diff --git a/apps/client/src/utils/formatters.ts b/apps/client/src/utils/formatters.ts
index ab1263a54..a7c9cceed 100644
--- a/apps/client/src/utils/formatters.ts
+++ b/apps/client/src/utils/formatters.ts
@@ -10,7 +10,7 @@ export function formatDateTime(date: string | Date | number | null | undefined,
         return "";
     }
 
-    const locale = options.get("formattingLocale") || options.get("locale") || navigator.language;
+    const locale = normalizeLocale(options.get("formattingLocale") || options.get("locale") || navigator.language);
 
     let parsedDate;
     if (typeof date === "string" || typeof date === "number") {
@@ -51,3 +51,12 @@ export function formatDateTime(date: string | Date | number | null | undefined,
 
     throw new Error("Incorrect state.");
 }
+
+export function normalizeLocale(locale: string) {
+    locale = locale.replaceAll("_", "-");
+    switch (locale) {
+        case "cn": return "zh-CN";
+        case "tw": return "zh-TW";
+        default: return locale;
+    }
+}