diff --git a/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp b/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp
--- a/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp
+++ b/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp
@@ -7,12 +7,13 @@
 //===----------------------------------------------------------------------===//
 
 // REQUIRES: host-has-gdb-with-python
+// REQUIRES: locale.en_US.UTF-8
 // UNSUPPORTED: libcpp-has-no-localization
 // UNSUPPORTED: c++03
 
 // RUN: %{cxx} %{flags} %s -o %t.exe %{compile_flags} -g %{link_flags}
 // Ensure locale-independence for unicode tests.
-// RUN: %{gdb} -nx -batch -iex "set autoload off" -ex "source %S/../../../utils/gdb/libcxx/printers.py" -ex "python register_libcxx_printer_loader()" -ex "source %S/gdb_pretty_printer_test.py" %t.exe
+// RUN: env LANG=en_US.UTF-8 %{gdb} -nx -batch -iex "set autoload off" -ex "source %S/../../../utils/gdb/libcxx/printers.py" -ex "python register_libcxx_printer_loader()" -ex "source %S/gdb_pretty_printer_test.py" %t.exe
 
 #include <bitset>
 #include <deque>
@@ -658,6 +659,7 @@
   string_test();
   a_namespace::string_view_test();
 
+  u16string_test();
   u32string_test();
   tuple_test();
   unique_ptr_test();
diff --git a/libcxx/utils/ci/Dockerfile b/libcxx/utils/ci/Dockerfile
--- a/libcxx/utils/ci/Dockerfile
+++ b/libcxx/utils/ci/Dockerfile
@@ -44,6 +44,7 @@
 # Install various tools used by the build or the test suite
 RUN apt-get update && apt-get install -y ninja-build python3 python3-sphinx python3-distutils git gdb
 RUN apt-get update && apt-get install -y libc6-dev-i386 # Required to cross-compile to 32 bits
+RUN apt-get update && apt-get install -y language-pack-en # To get en_US.UTF-8 local for gdb tests
 
 # Install Clang <latest>, <latest-1> and ToT, which are the ones we support.
 ENV LLVM_LATEST_VERSION=12