Default formats should not be based on timezones

[Pierre Equoy]

Image: Disco Dingo (19.04)

Steps to reproduce
------------------

1. Boot live USB
2. Install the image
3. Select "English" as language
4. Select "English (US)" as keyboard layout
5. Select "Taipei" in the "Where are you?" screen
6. Complete installation and check the time and date format used in the notification area, as well as in Settings > Region & Language

Expected result
---------------

The date and time format (as well as numbers etc.) is based on my language and/or keyboard layout

Actual result
-------------

The date and time format (as well as numbers etc.) is set to "Taiwan (Chinese, Literary)".

Rationale
---------

I'm a French national living in Taiwan and using Ubuntu in English. When installing Ubuntu, I always assume the "Where are you?" step is to set your timezone and nothing else. However, it seems to be used to also set the date, time and number formats, which for me don't make that much sense.

Moreover, it affects a lot of things (terminal outputs, etc.) and it's not that trivial to find the right menu to change this setting (I always have to go in the Settings panel and spend a good amount of time figuring out it's actually in the "Region & Language" panel)

Suggestions
-----------

1. Add a step in Ubiquity to select the formats to use. It could be pre-filled with guessed information (for instance from the timezone, as it's done today, or from the keyboard layout), but at least it would give an option for the user prior to installing.
2. Use the keyboard layout to determine what formats to use. This could work but could be tricky for some layouts like Dvorak...

Additional information
----------------------

This is my locale information right after installing.

$ locale
LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC=lzh_TW
LC_TIME=lzh_TW
LC_COLLATE="en_US.UTF-8"
LC_MONETARY=lzh_TW
LC_MESSAGES="en_US.UTF-8"
LC_PAPER=lzh_TW
LC_NAME=lzh_TW
LC_ADDRESS=lzh_TW
LC_TELEPHONE=lzh_TW
LC_MEASUREMENT=lzh_TW
LC_IDENTIFICATION=lzh_TW
LC_ALL=

Also, please see attached screenshots for the different installation steps and results.

ProblemType: Bug
DistroRelease: Ubuntu 19.04
Package: ubiquity (not installed)
ProcVersionSignature: Ubuntu 5.0.0-20.21-generic 5.0.8
Uname: Linux 5.0.0-20-generic x86_64
ApportVersion: 2.20.10-0ubuntu27
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Tue Jul 2 17:04:11 2019
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash ---
InstallationDate: Installed on 2019-07-02 (0 days ago)
InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Release amd64 (20190416)
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)