This should be checked with fresh FileZilla installation, but I cannot try it right now. On a side note, 'Language' (or 'Language/Locale') shouldn't be unselected upon installation, but set to 'Default system language'. Show icon preview, Displays thumbnails for available file formats in the item list. 'Language' should be 'Language/Locale', and for Date/Time 'Use system defaults' should be 'Use locale defaults'. ForkLift is a robust FTP/SFTP/WebDAV/Amazon S3/Backblaze B2/Google. I think that the core problem here is mislabeling. When set to 'Use system defaults', should it use system defaults or selected Language/Locale defaults? But still, there are separate settings for date/time format. The technically correct term would be 'Locale', though as most users would not understand it, it's labelled 'Language' instead. For example, there is a log entry 'T10:53:00.059Z << FTP Session 140.' In my case, local time would be T13:53:00.059 +0300. I'm not sure just why does the language selection affects date/time format? I'm not sure now, I believe i was using version 3.9.0.5 (fresh Windows installation), but settings were backed up before reinstallation, and I regulary updated versions. which is the version you first used with your current user profile without ever deleting the settings? How old is your current installation of FileZilla, ie.

I just checked language, and no language was set, strange.

Filezilla log files change time format