The page at:

https://picard.musicbrainz.org/docs/build-windows/

needs to have the following text revised:

Download and install gettext from http://gnuwin32.sourceforge.net/packages/gettext.htm.

Add the gettext folder to %PATH% (default C:\Program Files\GnuWin32\bin or C:\Program Files (x86)\GnuWin32\bin)

The issue is the gettext lib referenced is no longer able to complete the language mapping build process. It appears to be outdated.  The Invisible Man has provided a solution in:

https://tickets.metabrainz.org/browse/PICARD-1264

I tested his solution in setting up my own dev env, and can confirm it worked for me as well. However, the docs are still steering people into the weeds.

I would suggest the docs should be updated per his solution, or some equivalent.