pu=strftime "en août" breaks fileencoding

[harriott]

Problem

In August, on a French system, in a utf-8 file, :pu=strftime('%B') puts ao<fb>t where that <fb> is some kind of holding character. Saving and reloading the file then switches it to fileencoding=latin1, and un-undoably replaces existing utf-8 glyphs with multi-character latin1 encodings.

Steps to reproduce

nvim --clean empty_utf8_file :se fenc=utf8 :pu=strftime('%B') :w :e :se fenc

Expected behavior

In August in France, :pu=strftime('%B') should :put "août" with no consequent switching of fileencoding to latin1.

Neovim version (nvim -v)

NVIM v0.10.1

Vim (not Nvim) behaves the same?

no, vim 9.1

Operating system/version

Windows 10 Pro

Terminal name/version

Windows Terminal v1.20.11781.0

$TERM environment variable

not applicable

Installation

winget add Neovim.Neovim