diff --git a/build/cmake/tests/base/CMakeLists.txt b/build/cmake/tests/base/CMakeLists.txt
index 71ca50e243..9fb576c1d6 100644
--- a/build/cmake/tests/base/CMakeLists.txt
+++ b/build/cmake/tests/base/CMakeLists.txt
@@ -106,6 +106,8 @@ if(wxUSE_XML)
 endif()
 
 set(TEST_DATA
+    intl/en_GB/internat.mo
+    intl/en_GB/internat.po
     intl/fr/internat.mo
     intl/fr/internat.po
     intl/ja/internat.mo
diff --git a/tests/Makefile.in b/tests/Makefile.in
index 760d178820..f9c14e47b6 100644
--- a/tests/Makefile.in
+++ b/tests/Makefile.in
@@ -463,7 +463,7 @@ COND_MONOLITHIC_1___WXLIB_MONO_p = \
 
 ### Targets: ###
 
-all: test$(EXEEXT) $(__test_drawing___depname) $(__test_drawingplugin___depname) $(__test_gui___depname) $(__test_gui_bundle___depname) $(__test_allheaders___depname) $(__test_allheaders_bundle___depname) data data-image-sample data-images fr ja
+all: test$(EXEEXT) $(__test_drawing___depname) $(__test_drawingplugin___depname) $(__test_gui___depname) $(__test_gui_bundle___depname) $(__test_allheaders___depname) $(__test_allheaders_bundle___depname) data data-image-sample data-images en_GB fr ja
 
 install: 
 
@@ -602,6 +602,18 @@ data-images:
 	esac; \
 	done
 
+en_GB: 
+	@mkdir -p ./intl/en_GB
+	@for f in internat.po internat.mo; do \
+	if test ! -f ./intl/en_GB/$$f -a ! -d ./intl/en_GB/$$f ; \
+	then x=yep ; \
+	else x=`find $(srcdir)/intl/en_GB/$$f -newer ./intl/en_GB/$$f -print` ; \
+	fi; \
+	case "$$x" in ?*) \
+	cp -pRf $(srcdir)/intl/en_GB/$$f ./intl/en_GB ;; \
+	esac; \
+	done
+
 fr: 
 	@mkdir -p ./intl/fr
 	@for f in internat.po internat.mo; do \
@@ -1278,4 +1290,4 @@ failtest_allheaders:
 @IF_GNU_MAKE@-include ./.deps/*.d
 
 .PHONY: all install uninstall clean distclean test_gui_bundle \
-	test_allheaders_bundle data data-image-sample data-images fr ja
+	test_allheaders_bundle data data-image-sample data-images en_GB fr ja
diff --git a/tests/intl/en_GB/internat.mo b/tests/intl/en_GB/internat.mo
new file mode 100644
index 0000000000..2089093322
Binary files /dev/null and b/tests/intl/en_GB/internat.mo differ
diff --git a/tests/intl/en_GB/internat.po b/tests/intl/en_GB/internat.po
new file mode 100644
index 0000000000..1bdced1767
--- /dev/null
+++ b/tests/intl/en_GB/internat.po
@@ -0,0 +1,18 @@
+# SOME DESCRIPTIVE TITLE.
+# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
+# This file is distributed under the same license as the PACKAGE package.
+# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
+#
+#, fuzzy
+msgid ""
+msgstr ""
+"Project-Id-Version: \n"
+"POT-Creation-Date: 2003-10-04 23:10+0200\n"
+"PO-Revision-Date: 2024-02-13 13:25+0100\n"
+"Last-Translator: \n"
+"Language-Team: \n"
+"Language: en_GB\n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Plural-Forms: nplurals=2; plural=(n != 1);\n"
diff --git a/tests/intl/intltest.cpp b/tests/intl/intltest.cpp
index 9b14175fce..a504a9edaa 100644
--- a/tests/intl/intltest.cpp
+++ b/tests/intl/intltest.cpp
@@ -19,6 +19,7 @@
 
 #include "wx/intl.h"
 #include "wx/uilocale.h"
+#include "wx/scopeguard.h"
 
 #include "wx/private/glibc.h"
 
@@ -241,8 +242,9 @@ void IntlTestCase::IsAvailable()
 
 TEST_CASE("wxTranslations::AddCatalog", "[translations]")
 {
-    // We currently have translations for French and Japanese in this test
-    // directory, check that loading those succeeds but loading others doesn't.
+    // We currently have translations for British English, French and Japanese
+    // in this test directory, check that loading those succeeds but loading
+    // others doesn't.
     wxFileTranslationsLoader::AddCatalogLookupPathPrefix("./intl");
 
     const wxString domain("internat");
@@ -252,11 +254,12 @@ TEST_CASE("wxTranslations::AddCatalog", "[translations]")
     SECTION("All")
     {
         auto available = trans.GetAvailableTranslations(domain);
-        REQUIRE( available.size() == 2 );
+        REQUIRE( available.size() == 3 );
 
         available.Sort();
-        CHECK( available[0] == "fr" );
-        CHECK( available[1] == "ja" );
+        CHECK( available[0] == "en_GB" );
+        CHECK( available[1] == "fr" );
+        CHECK( available[2] == "ja" );
     }
 
     SECTION("French")
@@ -287,6 +290,60 @@ TEST_CASE("wxTranslations::AddCatalog", "[translations]")
     }
 }
 
+TEST_CASE("wxTranslations::GetBestTranslation", "[translations]")
+{
+    wxFileTranslationsLoader::AddCatalogLookupPathPrefix("./intl");
+
+    const wxString domain("internat");
+
+    wxTranslations trans;
+    wxON_BLOCK_EXIT1( wxUnsetEnv, "WXLANGUAGE" );
+
+    SECTION("ChooseLanguage")
+    {
+        // Simple case.
+        wxSetEnv("WXLANGUAGE", "fr:en");
+        CHECK( trans.GetBestTranslation(domain) == "fr" );
+        CHECK( trans.GetBestAvailableTranslation(domain) == "fr" );
+
+        // Choose 2nd language _and_ its base form.
+        wxSetEnv("WXLANGUAGE", "cs:fr_CA:en");
+        CHECK( trans.GetBestTranslation(domain) == "fr" );
+        CHECK( trans.GetBestAvailableTranslation(domain) == "fr" );
+    }
+
+    SECTION("EnglishHandling")
+    {
+        // Check that existing en_GB file isn't used for msgid language.
+        wxSetEnv("WXLANGUAGE", "en_US");
+
+        CHECK( trans.GetBestTranslation(domain) == "en" );
+        // GetBestAvailableTranslation() will wrongly return "en_GB", don't test that.
+
+        wxSetEnv("WXLANGUAGE", "es:en");
+        CHECK( trans.GetBestTranslation(domain) == "en" );
+        // GetBestAvailableTranslation() will wrongly return "en_GB", don't test that.
+
+        // And that it is used when it should be
+        wxSetEnv("WXLANGUAGE", "en_GB");
+        CHECK( trans.GetBestTranslation(domain) == "en_GB" );
+        CHECK( trans.GetBestAvailableTranslation(domain) == "en_GB" );
+
+    }
+
+    SECTION("DontSkipMsgidLanguage")
+    {
+        // Check that msgid language will be used if it's the best match.
+        wxSetEnv("WXLANGUAGE", "cs:en:fr");
+        CHECK( trans.GetBestTranslation(domain) == "en" );
+
+        // ...But won't be used if there's a suitable translation file.
+        wxSetEnv("WXLANGUAGE", "fr:en:cs");
+        CHECK( trans.GetBestTranslation(domain) == "fr" );
+        CHECK( trans.GetBestAvailableTranslation(domain) == "fr" );
+    }
+}
+
 TEST_CASE("wxLocale::Default", "[locale]")
 {
     const int langDef = wxUILocale::GetSystemLanguage();
diff --git a/tests/makefile.gcc b/tests/makefile.gcc
index 048f3fc3ed..8cbaed0a1e 100644
--- a/tests/makefile.gcc
+++ b/tests/makefile.gcc
@@ -512,7 +512,7 @@ $(OBJS):
 
 ### Targets: ###
 
-all: $(OBJS)\test.exe $(__test_drawing___depname) $(__test_drawingplugin___depname) $(__test_gui___depname) $(__test_allheaders___depname) data data-image-sample data-images fr ja
+all: $(OBJS)\test.exe $(__test_drawing___depname) $(__test_drawingplugin___depname) $(__test_gui___depname) $(__test_allheaders___depname) data data-image-sample data-images en_GB fr ja
 
 clean: 
 	-if exist $(OBJS)\*.o del $(OBJS)\*.o
@@ -572,6 +572,10 @@ data-images:
 	if not exist image mkdir image
 	for %%f in (bitfields.bmp bitfields-alpha.bmp 8bpp-colorsused-large.bmp 8bpp-colorsused-negative.bmp rle4-delta-320x240.bmp rle8-delta-320x240.bmp rle8-delta-320x240-expected.bmp horse_grey.bmp horse_grey_flipped.bmp horse_rle4.bmp horse_rle4_flipped.bmp horse_rle8.bmp horse_rle8_flipped.bmp horse_bicubic_50x50.png horse_bicubic_100x100.png horse_bicubic_150x150.png horse_bicubic_300x300.png horse_bilinear_50x50.png horse_bilinear_100x100.png horse_bilinear_150x150.png horse_bilinear_300x300.png horse_box_average_50x50.png horse_box_average_100x100.png horse_box_average_150x150.png horse_box_average_300x300.png cross_bicubic_256x256.png cross_bilinear_256x256.png cross_box_average_256x256.png cross_nearest_neighb_256x256.png paste_input_background.png paste_input_black.png paste_input_overlay_transparent_border_opaque_square.png paste_input_overlay_transparent_border_semitransparent_circle.png paste_input_overlay_transparent_border_semitransparent_square.png paste_result_background_plus_circle_plus_square.png paste_result_background_plus_overlay_transparent_border_opaque_square.png paste_result_background_plus_overlay_transparent_border_semitransparent_square.png paste_result_no_background_square_over_circle.png wx.png toucan.png toucan_hue_0.538.png toucan_sat_-0.41.png toucan_bright_-0.259.png toucan_hsv_0.538_-0.41_-0.259.png toucan_light_46.png toucan_dis_240.png toucan_grey.png toucan_mono_255_255_255.png width-times-height-overflow.bmp width_height_32_bit_overflow.pgm bad_truncated.gif) do if not exist image\%%f copy .\image\%%f image
 
+en_GB: 
+	if not exist $(OBJS)\intl\en_GB mkdir $(OBJS)\intl\en_GB
+	for %%f in (internat.po internat.mo) do if not exist $(OBJS)\intl\en_GB\%%f copy .\intl\en_GB\%%f $(OBJS)\intl\en_GB
+
 fr: 
 	if not exist $(OBJS)\intl\fr mkdir $(OBJS)\intl\fr
 	for %%f in (internat.po internat.mo) do if not exist $(OBJS)\intl\fr\%%f copy .\intl\fr\%%f $(OBJS)\intl\fr
@@ -1201,7 +1205,7 @@ $(OBJS)\test_allheaders_allheaders.o: ./allheaders.cpp
 $(OBJS)\test_allheaders_testableframe.o: ./testableframe.cpp
 	$(CXX) -c -o $@ $(TEST_ALLHEADERS_CXXFLAGS) $(CPPDEPS) $<
 
-.PHONY: all clean data data-image-sample data-images fr ja
+.PHONY: all clean data data-image-sample data-images en_GB fr ja
 
 
 SHELL := $(COMSPEC)
diff --git a/tests/makefile.vc b/tests/makefile.vc
index 41c1452831..2ee5ebb7d3 100644
--- a/tests/makefile.vc
+++ b/tests/makefile.vc
@@ -792,7 +792,7 @@ $(OBJS):
 
 ### Targets: ###
 
-all: $(OBJS)\test.exe $(__test_drawing___depname) $(__test_drawingplugin___depname) $(__test_gui___depname) $(__test_allheaders___depname) data data-image-sample data-images fr ja
+all: $(OBJS)\test.exe $(__test_drawing___depname) $(__test_drawingplugin___depname) $(__test_gui___depname) $(__test_allheaders___depname) data data-image-sample data-images en_GB fr ja
 
 clean: 
 	-if exist $(OBJS)\*.obj del $(OBJS)\*.obj
@@ -863,6 +863,10 @@ fr:
 	if not exist $(OBJS)\intl\fr mkdir $(OBJS)\intl\fr
 	for %f in (internat.po internat.mo) do if not exist $(OBJS)\intl\fr\%f copy .\intl\fr\%f $(OBJS)\intl\fr
 
+en_GB: 
+	if not exist $(OBJS)\intl\en_GB mkdir $(OBJS)\intl\en_GB
+	for %f in (internat.po internat.mo) do if not exist $(OBJS)\intl\en_GB\%f copy .\intl\en_GB\%f $(OBJS)\intl\en_GB
+
 ja: 
 	if not exist $(OBJS)\intl\ja mkdir $(OBJS)\intl\ja
 	for %f in (internat.po internat.mo) do if not exist $(OBJS)\intl\ja\%f copy .\intl\ja\%f $(OBJS)\intl\ja
diff --git a/tests/test.bkl b/tests/test.bkl
index 67ce2c10c1..323ce14c9d 100644
--- a/tests/test.bkl
+++ b/tests/test.bkl
@@ -429,6 +429,7 @@
         <files>internat.po internat.mo</files>
     </template>
 
+    <wx-data id="en_GB" template="catalog"/>
     <wx-data id="fr" template="catalog"/>
     <wx-data id="ja" template="catalog"/>