fix: sanitize Accept-Language locale parsing (#746)

* fix: sanitize Accept-Language locale parsing

* refactor(accept-language): prefer the highest quality language

app/server/lib/functions/root-loader-data.ts

@@ -2,6 +2,7 @@ import { createServerFn } from "@tanstack/react-start";
 import { getCookie, getRequestHeaders } from "@tanstack/react-start/server";
 import { THEME_COOKIE_NAME } from "~/client/components/theme-provider";
 import type { DateFormatPreference, TimeFormatPreference } from "~/client/lib/datetime";
+import { getLocaleFromAcceptLanguage } from "~/server/lib/accept-language";
 import { auth } from "~/server/lib/auth";
 
 export const getRootLoaderData = createServerFn({ method: "GET" }).handler(async () => {
@@ -12,7 +13,7 @@ export const getRootLoaderData = createServerFn({ method: "GET" }).handler(async
 
 	return {
 		theme: (themeCookie === "light" ? "light" : "dark") as "light" | "dark",
-		locale: (acceptLanguage?.split(",")[0] || "en-US") as string,
+		locale: getLocaleFromAcceptLanguage(acceptLanguage),
 		timeZone: process.env.TZ || Intl.DateTimeFormat().resolvedOptions().timeZone || "UTC",
 		dateFormat: (session?.user.dateFormat ?? "MM/DD/YYYY") as DateFormatPreference,
 		timeFormat: (session?.user.timeFormat ?? "12h") as TimeFormatPreference,