I just recently checked my updates and updated Filezilla from v. 3.8.x to the latest, 22.214.171.124. My preferences were to use it in my "default system language", i.e. French, and things worked correctly before the version update. I did the update through the semi-automatic menu option: Check for updates.
When I start Filezilla 126.96.36.199, I receive a sybillic message: "Can't load DLL" and I have to use the default language, i.e. English. Moreover, if I go in "Settings" and try to change the language, there is only one choice available: "Default system language" and Filezilla works in English.
Ironically, I also have a computer where the desktop version of Filezilla was installed and has been upgraded, and all languages are available, so the problem is specific to Filezilla Portable.
I reinstalled Filezilla Portable 188.8.131.52 from scratch and I now have access to all languages, so it seems to be a problem specific to the automatic updates.