The Win64 builds have only been on the Nightly (or rather Daily) channel for QA testing. The Win64 builds is not needed like 64-bit builds for Max OSX and 64-bit was.

If there was going to be Win64 builds of Thunderbird for Release then it would have been on Beta channel for a while. No Win64 builds in http://archive.mozilla.org/pub/thunderbird/releases/60.0b2/

The Thunderbird community does not have the resources that Mozilla has for Firefox. https://blog.mozilla.org/thunderbird/2017/05/thunderbirds-future-home/

Before Mozilla had Win64 for Firefox Releases since 42.0 (on www.mozilla.org/firefox/all/) the Win64 builds before were mainly for QA and to catch breakage as it is possible to break Win64 builds without breaking the 32-bit builds when doing checkins.

I can confirm - wherever you saw this information, it is incorrect.

Wayne & James: OK. Thanks for your replies. Nevertheless, TB x64 on the Daily channel has been working without any bugs for me for a long time. It should be added to the release channel ASAP, IMHO. I understand the development/testing resource lack. TB is a superb E-mail program, and Mozilla's sidelining it as they have is a mistake, IMHO.

The various international help files for x32 should also work for the corresponding x64 versions. Guess the real problem is making & testing the various language executable & auxiliary packs, so I can understand that's probably pretty intimidating.