M12: regional formats (typed and displayed numbers, dates and times)

ROADMAP.md

@@ -2,7 +2,7 @@
 
 **Stage: alpha** · next: beta, ~25 points of "ready for real work" and ~160–240 h away
 
-> **Last reviewed:** 2026-10-11 · **Last updated:** 2026-10-12 · **Change:** minor (rows auto-fit oversized fonts on open and whole-row/column formatting) · **Target:** Microsoft Excel (Microsoft 365)
+> **Last reviewed:** 2026-10-11 · **Last updated:** 2026-10-12 · **Change:** minor (regional formats, `app.region`) · **Target:** Microsoft Excel (Microsoft 365)
 
 GridCraft aims at full Microsoft Excel parity, and at being better in places: faster, open (XLSX
 is the native format), fully scriptable by agents (MCP, control channel, CLI), and on the web.
@@ -93,7 +93,8 @@ The ribbon is translated into Japanese, Simplified Chinese, Korean, Brazilian Po
 and German (266–268 labels each, ~12% of ~2,200 strings; merged 10-10 in #31, #104, #82, German
 added 10-11), the
 interface follows the system language, and CJK, Thai and Hebrew text falls back to system fonts
-(#38). Dialogs, menus and messages are English; formulas and number formats are en-US only.
+(#38). Dialogs, menus and messages are English; formulas are en-US (plus Spanish). Numbers, dates
+and times follow a Regional format setting (15 regions; File › Options, `app.region`).
 Localized German formulas and numbers are in PR #163. Detail: [localization-parity.md](docs/localization-parity.md).
 
 | Language | Code | Status | UI strings |
@@ -165,6 +166,7 @@ Ranked; estimates in Opus 5.5 agent-hours. Detail and the full beta-gate list in
 | 2026-10-11 | XLSX pass-through: custom XML, external links, connections, query tables, printer settings, form/ActiveX controls and OLE objects are kept on save (#330, #324) |
 | 2026-10-11 | Data › Forecast › Forecast Sheet: a new sheet with the history, FORECAST.ETS forecast, confidence bounds, statistics and a chart (#322) |
 | 2026-10-11 | Startup no longer panics on a system font egui can't parse: fonts are validated and skipped (#226) |
+| 2026-10-11 | Regional formats: File › Options › Regional format (`app.region`) changes how numbers, dates and times are typed and shown, for 15 regions |
 | 2026-10-11 | Ctrl+drag on the fill handle swaps copying and extending a series (#264) |
 | 2026-10-11 | Odd-period bond functions ODDFPRICE, ODDFYIELD, ODDLPRICE, ODDLYIELD: Financial 55 / 55 (#275) |
 | 2026-10-11 | PERCENTOF and EUROCONVERT worksheet functions (#279) |
@@ -201,6 +203,7 @@ Ranked; estimates in Opus 5.5 agent-hours. Detail and the full beta-gate list in
 | 2026-10-12 | minor | Ink preservation across XLSX save/reopen (ink portion of #551) |
 | 2026-10-12 | minor | Desktop File > Print now discovers printers and submits PDF jobs through pinned craft-print with printer choice, copies, duplex and grayscale; browser printing and PDF export remain available. Remaining print parity includes page ranges and driver-specific tray/options UI; physical printer fidelity needs hardware validation. |
 | 2026-10-11 | minor | Password-encrypted workbooks open (#11); progress log row |
+| 2026-10-11 | minor | Regional formats (`app.region`); progress log row |
 | 2026-10-11 | minor | Forecast Sheet (#322); progress log row |
 | 2026-10-11 | minor | Worksheet functions 505 / 523 (ODD* bond functions); progress log row |
 | 2026-10-11 | minor | Worksheet functions 503 / 523 (PERCENTOF, EUROCONVERT); progress log row |

apps/gridcraft-web/src/web.rs

@@ -58,6 +58,12 @@ pub fn start() {
                     ) {
                         app.ui.language = browser;
                     }
+                    // The browser's regional format too, with the same CJK exception: month names and AM/PM
+                    // words of those regions need a CJK font the web build doesn't have.
+                    let region = gridcraft_ui_egui::i18n::system_region();
+                    if !matches!(region.tag, "ja-JP" | "ko-KR" | "zh-CN" | "zh-TW") {
+                        let _ = app.session.set_region(region.tag);
+                    }
                     SheetApp::setup_context_for_language(&cc.egui_ctx, false, app.ui.language);
                     if let Some(bridge) = &app_bridge {
                         if let Some(author) = query_param("author") {

apps/gridcraft/src/main.rs

@@ -105,6 +105,9 @@ fn load_prefs(app: &mut SheetApp) {
     app.ui.language = gridcraft_ui_egui::i18n::Language::system();
     // ...and its light or dark appearance (#239), until a theme is chosen and saved in ui.json.
     app.ui.system_theme = true;
+    // ...and its regional format (separators, date order), until one is chosen and saved in prefs.json.
+    app.session.prefs.region = gridcraft_ui_egui::i18n::system_region().tag.into();
+    app.session.apply_region();
     let Some(dir) = config_dir() else { return };
     if let Ok(b) = std::fs::read(dir.join("ui.json"))
         && let Ok(ui) = serde_json::from_slice::<gridcraft_ui_egui::UiState>(&b)
@@ -115,9 +118,16 @@ fn load_prefs(app: &mut SheetApp) {
         app.ui.language = language;
     }
     if let Ok(b) = std::fs::read(dir.join("prefs.json"))
-        && let Ok(p) = serde_json::from_slice(&b)
+        && let Ok(mut p) = serde_json::from_slice::<gridcraft_engine::Prefs>(&b)
     {
+        // A prefs.json from before regions existed has no region: keep the system's.
+        let saved_region =
+            serde_json::from_slice::<serde_json::Value>(&b).ok().is_some_and(|v| v.get("region").is_some_and(serde_json::Value::is_string));
+        if !saved_region {
+            p.region = app.session.prefs.region.clone();
+        }
         app.session.prefs = p;
+        app.session.apply_region();
     }
 }
 

crates/core/src/lib.rs

@@ -1,13 +1,15 @@
 //! GridCraft core types: cell addresses, values and Excel's coercion rules, error values,
-//! date serials and typed-input parsing. No dependencies on the rest of the workspace.
+//! date serials, regional formats and typed-input parsing. No dependencies on the rest of the workspace.
 #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
 #![forbid(unsafe_code)]
 
 pub mod addr;
 pub mod date;
 pub mod parse;
+pub mod region;
 pub mod value;
 
 pub use addr::{CellRef, MAX_COLS, MAX_ROWS, RangeRef, col_to_letters, letters_to_col};
 pub use date::DateSystem;
+pub use region::Region;
 pub use value::{Array, CellError, Value, compare, compare_numbers, compare_text, number_to_text, sort_compare};