I would like to suggest adding LC_ALL=C.UTF-8 in qt6.port.mk.
The reason for this is to get rid of the following warning during
the build:

# Detected locale "C" with character encoding "US-ASCII", which is not UTF-8.
# Qt depends on a UTF-8 locale, and has switched to "C.UTF-8" instead.

In the end we have C.UTF-8 anyway.

OK?

Index: qt6.port.mk
===================================================================
RCS file: /cvs/ports/x11/qt6/qt6.port.mk,v
diff -u -p -r1.12 qt6.port.mk
--- qt6.port.mk	22 May 2025 08:52:31 -0000	1.12
+++ qt6.port.mk	2 Aug 2025 19:24:21 -0000
@@ -61,6 +61,11 @@ COMPILER ?= base-clang ports-gcc
 ONLY_FOR_ARCHS ?= ${CXX11_ARCHS}
 .endif
 
+# Detected locale "C" with character encoding "US-ASCII", which is not UTF-8.
+# Qt depends on a UTF-8 locale, and has switched to "C.UTF-8" instead.
+CONFIGURE_ENV +=	LC_ALL=C.UTF-8
+MAKE_ENV +=		LC_ALL=C.UTF-8
+
 .include "Makefile.version"
 
 MODQT6_VERSION =	${QT6_VERSION}