SUMMARY

This issue has been observed in all versions I tested, including the <https://invent.kde.org/graphics/krita/-/tree/bd0a2ffa95c16e27fff4618e1d13fa2aeefa6c8e> and version 5.2.11.

On Windows with a CJK locale, if the "Beta: Use UTF-8 for worldwide language support" option in Control Panel -> Region -> Administrative -> Language for non-Unicode programs is not enabled, Krita fails to execute FFmpeg commands containing CJK characters, preventing animations from being exported correctly.

In theory, this issue may affect all users with CJK languages. I have only tested it in a Simplified Chinese environment, where the system default encoding is GBK rather than UTF-8. Other CJK language environments may use different encodings.

Problematic characters (original UTF-8): (测试)  (Hex: E6 B5 8B E8 AF 95)
Characters actually passed by Krita to Windows (decoded as GBK): (娴嬭瘯)

STEPS TO REPRODUCE
1. Open Krita
2. Open Krita File
3. File -> Render Animation
4. Check "Export as Video" and make sure the export path contains at least one CJK character, then click "OK" to start the export.

OBSERVED RESULT

Frames exported successfully, but FFmpeg conversion failed.


SOFTWARE/OS VERSIONS
Windows: Windows10 amd64 (Kernel version: 19045.6282) (It seems to have nothing to do with the Windows version)

ADDITIONAL INFORMATION

FFmpeg logs:
Z:/Krita-Night/bin/ffmpeg.exe -hide_banner -y -y -r 24 -start_number 0 -start_number_range 1 -i C:/Users/SpiritIce/Pictures/frame%04d.png -c:v libopenh264 -b:v 5000k C:/Users/SpiritIce/Pictures/测试.mp4
=====================================================
Input #0, image2, from 'C:/Users/SpiritIce/Pictures/frame%04d.png':
  Duration: 00:00:04.04, start: 0.000000, bitrate: N/A
  Stream #0:0: Video: png, rgba(pc, gbr/unknown/unknown), 1756x1240 [SAR 11811:11811 DAR 439:310], 25 fps, 25 tbr, 25 tbn
[out#0/mp4 @ 000002a014696380] Error opening output C:/Users/SpiritIce/Pictures/测试.mp4: Invalid argument
Error opening output file C:/Users/SpiritIce/Pictures/测试.mp4.
Error opening output files: Invalid argument