PsychoPy 2026.2.4 fails to start on Japanese Windows 11 due to UTF-8 / cp932 issue

Other
1

FYI

PsychoPy 2026.2.4
Windows 11 Japanese

PsychoPy would not start at all after installation.

Running:

import psychopy.app
psychopy.app.startApp()

raised:

UnicodeDecodeError: ‘cp932’ codec can’t decode byte 0xef …

The problem was in:

Lib/site-packages/i18next/base.py

Changing the file opening to:

encoding=“utf-8-sig”

resolved the issue.

Locale:
(‘ja_JP’, ‘cp932’)

2

Hi, agein.
Additional note:

After fixing the UTF-8 issue, PsychoPy starts.

However, the GUI remains entirely in English.

I checked:

D:\Program Files\PsychoPy\Lib\site-packages\psychopy\localization\locales\ja-JP.json

and it only contains one translation entry:

“Welcome to PsychoPy!”

For example:

from psychopy.localization import _translate
print(_translate(“File”))

returns:

File

so it appears the Japanese localization file is largely empty.

3

Hello @lupus_Canis

That could well be. If you want to contribute a Japanese localization take a look here Translations — PsychoPy®

Best wishes Jens

4

Thank you. I highlighted this post to @TParsons who has discovered a bug which should be fixed in the next release (2026.2.5 coming soon).