Language didn't work only with Vietnamese

[hnguyentcc]

Information about bug

Hi team,

I'm facing an issue about the language pack didnt work.
Description
Even though Vietnamese (vi) is available in the Languages doctype and set as both System Language and User Language, the UI does not switch to Vietnamese. Instead, it falls back to English. Other languages (e.g., German de) work fine.

Steps to Reproduce

Install and run latest frappe, erpnext, and hrms apps on Docker.
Enable Vietnamese (vi) in Languages doctype.
Set System Settings → Language = Vietnamese (vi).
Set User (Administrator) → Language = Vietnamese (vi).
Reload/clear cache.

Expected Behavior
The UI should render in Vietnamese if translations exist (similar to German).

Actual Behavior
The system refreshes but falls back to English. Vietnamese does not display anywhere in the UI.

Module

HR

Version

Frappe: 15.x.x-develop
ERPNext: 15.x.x-develop
HRMS: 16.0.0-dev

Installation method

docker

Relevant log output / Stack trace / Full Error Message.

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