fix(ui): configurable date locale (was hardcoded en-US)

CHANGELOG.md

@@ -13,6 +13,19 @@ semver-governed public surface — a breaking change to a seam is a major bump.
 
 ## [Unreleased]
 
+## [0.6.9] - 2026-07-29
+
+### Fixed
+- **Dates no longer force US format.** `formatDate` hardcoded the `"en-US"`
+  locale (and an English short month), so every deployment showed US-style
+  dates regardless of the viewer. It now formats numeric, day/month per the
+  configured locale, defaulting to the **viewer's browser locale**. A
+  deployment can pin it with the new **`setDateLocale(locale)`** (e.g.
+  `setDateLocale("de-CH")` for `DD.MM.YYYY` everywhere). `setDateLocale` and
+  `formatDate` are exported from the package.
+  Note: native `<input type="date">` pickers still render in the browser/OS
+  locale — that's the platform, not this formatter.
+
 ## [0.6.8] - 2026-07-29
 
 ### Added

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@lambda-development/erp-core",
-  "version": "0.6.8",
+  "version": "0.6.9",
   "description": "Frontend core of Lambda ERP — app shell, document/master pages, chat UI, reports, and extension registries.",
   "license": "Apache-2.0",
   "repository": {

frontend/src/index.ts

@@ -55,6 +55,10 @@ export type { ListContext } from "./lib/doc-list-context";
 export { configureBranding, getBranding } from "./lib/branding";
 export type { Branding } from "./lib/branding";
 
+// Date display locale (default: viewer's browser locale). Pin per deployment,
+// e.g. setDateLocale("de-CH").
+export { setDateLocale, formatDate } from "./lib/utils";
+
 // API client
 export { api, request, ApiError, configureApiBase } from "./api/client";
 

frontend/src/lib/utils.ts

@@ -20,13 +20,24 @@ export function formatNumber(value: number | null | undefined, decimals = 2) {
   }).format(value ?? 0);
 }
 
-/** Format a date string for display. */
+// Display locale for dates. Default: the viewer's browser locale — the old
+// hardcoded "en-US" forced US month/day order (and English month names) on
+// every deployment. A deployment can pin it, e.g. setDateLocale("de-CH") for
+// DD.MM.YYYY everywhere, regardless of the viewer's browser.
+let dateLocale: string | undefined;
+
+/** Pin the locale used by formatDate (undefined = the viewer's browser locale). */
+export function setDateLocale(locale: string | undefined) {
+  dateLocale = locale;
+}
+
+/** Format a date string for display (numeric, day-first per the locale). */
 export function formatDate(value: string | null | undefined) {
   if (!value) return "";
-  return new Date(value).toLocaleDateString("en-US", {
+  return new Date(value).toLocaleDateString(dateLocale, {
     year: "numeric",
-    month: "short",
-    day: "numeric",
+    month: "2-digit",
+    day: "2-digit",
   });
 }
 

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "lambda-erp"
-version = "0.6.8"
+version = "0.6.9"
 description = "Core ERP logic - accounting, sales, purchasing, inventory"
 readme = "README.md"
 license = "Apache-2.0"