Add locale option for FOAM_DATE_DAY_NAME_SHORT and FOAM_DATE_DAY_NAME variables

[yahsan2]

Problem

The FOAM_DATE_DAY_NAME_SHORT and FOAM_DATE_DAY_NAME variables use the system's default locale, which causes issues for users who want English day names (Mon, Tue, etc.) but have their OS set to a different language.

Currently, the code uses:

this.foamDate.toLocaleString('default', { weekday: 'short' })

This means users with Japanese, German, or other non-English locales get localized day names (e.g., "月" instead of "Mon").

Related Issues

• ${FOAM_DATE_*} variable expansion is dependent on system locale. #919 - Similar issue was reported and marked as fixed in v0.17.8, but the problem persists for FOAM_DATE_DAY_NAME_SHORT and FOAM_DATE_DAY_NAME variables
• Note from js template - supporting locale #1501 - Related locale support request for js templates

Why This Matters

The deprecated foam.openDailyNote.filenameFormat setting uses the dateformat library which outputs English day names regardless of locale. Users migrating to the new template-based approach (as recommended) lose this behavior.

For users who have existing daily notes with English day names like:

• 2023-01-22 (Sun).md
• 2023-01-23 (Mon).md

The new template system creates files with localized names:

• 2026-01-05 (月).md

This breaks consistency with existing notes.

Proposed Solution

Add a setting to specify the locale for date variables, for example:

{
  "foam.dateLocale": "en-US"
}

Or add new variables with explicit English locale:

• FOAM_DATE_DAY_NAME_EN
• FOAM_DATE_DAY_NAME_SHORT_EN

Environment

• Foam version: latest
• OS: macOS (Japanese locale)
• VS Code version: latest

Workaround

Currently using the deprecated foam.openDailyNote.filenameFormat setting, but this will be removed in future versions.

[riccardoferretti]

I like the idea of the setting.
The only thing I need to check is whether this requires additional dependencies or not (if it does it could be a pain)

[yahsan2]

Hi @riccardoferretti,

Thanks for the reply. I checked the codebase regarding the dependency concern.

No additional dependencies are required.

Current Implementation

In packages/foam-vscode/src/services/variable-resolver.ts:

case 'FOAM_DATE_DAY_NAME':
  value = Promise.resolve(
    this.foamDate.toLocaleString('default', { weekday: 'long' })
  );
  break;

Possible Solutions

Option 1: Native JavaScript (simplest)

Just make the locale parameter configurable:

const locale = config.get('foam.dateLocale') || 'default';
this.foamDate.toLocaleString(locale, { weekday: 'long' })

Option 2: Use existing dayjs dependency

Foam already has dayjs in package.json. It has built-in locale support:

import dayjs from 'dayjs';
import 'dayjs/locale/en';
dayjs(this.foamDate).locale('en').format('dddd'); // "Friday"

Either approach works without adding new npm packages.

[riccardoferretti]

From your second example (dayjs), you can see it also needs to import the locale, which as it's configurable becomes an issue. (so, no new packages, but different imports based on locale - probably for tree shaking)

I didn't know JS core includes locales, looking at the documentation it seems like it does without additional dependencies or imports.

So we should go for option 1

Would you like to implement the fix?

[tonn]

May be it's better to use existing date time formating library like date-fns? Without FOAM_DATE_* constants... just bypass template string to date-fns