Technically Impossible

Lets look at the weak link in your statement. Anything "Technically Impossible" basically means we haven't figured out how yet.

Multiple language support on Windows - input/output Japanese on English Windows.

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In iOS (iPhone OS, iPad OS) and Android, Settings for Language and Region is separated. And it can easily support input/output and screen in different language as Japanese input/output on English window. Windows 10 20H2 or later can be configured as well as the screenshot on the top of this post.

In iPad
f:id:espio999:20210414230243p:plain

In Android
f:id:espio999:20210414230337j:plain

Other than input/output of different languages, it has another benefit as common terminology. It can prevents embarrassing on communication and get richer search result from Internet.


The screenshot on the top of this post shows 5 categories of configuration below.

Windows display Language setting for Window parts as file menu, button, etc
Apps & websites Priority of languages in application supporting multiple languages
Regional format Format of calendar, currency, etc
Keyboard IME (Input Method Editor)
NOT for layout of keyboard
Speech Language for voice input/output

Even application deeply depending on Japanese can run without garbled fonts on Windows environment with

  • Windows display = English
  • App & websites = English

This is the example of "Microsoft/Shogakukan Bookshelf", the Japanese dictionary released in 90s. Even half-width Japanese fonts are rendered well.
f:id:espio999:20210414230506p:plain

"Regional format" works for currency, weights and measures, and date formats, et al. Even in common English regions as US, UK, Australia..., they use different format each others. Typically,

Order of date display Month / Day / Year
Day / Month / Year
AM, PM or 24 hours 00:00 ~ 12:00 AM / PM
00:00 ~ 23:59
Start date of week on calendar Monday
Sunday
Default sheet size Letter
A4

The screenshot at the top of this post shows configuration as

  • Windows and applications follows US format
  • Regional format follows UK style

One caution is, this configuration should not be set as a visual preference. Example date input in Excel, an user needs to follow specified order.
f:id:espio999:20210414230546p:plain
f:id:espio999:20210414230600p:plain

"Keyboard" is for IME, the input method, NOT for keyboard layout.
In a multi-language environment, an user needs to switch among languages. Even English input has the top priority, IME is switched with unintentional key presses. It is good idea to remember the following shortcuts to back to appropriate IME.

Switch IME
Switch language
Alt + Shift
Switch IME input Alt + ~

Off topic

The next blog introduces interesting topic. It says Japanese version Windows with English configuration is not equal of Original English Windows.

「日本語版Windowsを英語化したOS」と「英語版Windows OS」は等価でない

dev.classmethod.jp

Actually, it is true.
f:id:espio999:20210414231111p:plain

These configuration is only for appearance, not for SystemLocale. Some application installers checks SystemLocale and install its appropriate language version, or doesn't allow install to different language version.
docs.microsoft.com

In case of the later, as long as keeping original SystemLocale, switching appearance to English style is harmless for installing Japanese version application.
But it doesn't ensure safety for everything. What referred for switching language is depends on program. Example, web browser switch language on web site based on its own language settings.

In case of the later, as long as keeping original SystemLocale, switching appearance to English style is harmless for installing Japanese version application.
But it doesn't ensure safety for everything. What referred for switching language is depends on program. Example, web browser switch language on web site based on its own language settings.

The official information related to display and language is scattered as followings, it is difficult to grasp them in an integrated manner.

  • Desktop and other operational systems
  • Application development system

The following is a list of references.