Installing bitcoin-core in Arch Linux (VirtualBox) returns: unknown location(0): fatal error: in runtime error: _S_create_c_locale name not valid

I'd like to maintain a BTC node / wallet on a VM within VirtualBox. For this I installed Arch Linux, manually. The process wasn't the smoothest experience, but I got it working, eventually. Then I used this guide to install _yay_, successfully. I went ahead and tried to install _bitcoin-core_ by running yay -Sa bitcoin-core --answerclean y --answerdiff n. The installation takes long and fails, eventually. After a lot of lines starting with CXX I got these lines:

==> Starting check()...
  -> Testing ...
Making check in src
make[1] : Entering directory '/home/user/.cache/yay/bitcoin-core/src/bitcoin-0.21.0/src'
make[2] : Entering directory '/home/user/.cache/yay/bitcoin-core/src/bitcoin-0.21.0/src'
make: Entering directory '/home/user/.cache/yay/bitcoin-core/src/bitcoin-0.21.0'
make: Leaving directory '/home/user/.cache/yay/bitcoin-core/src/bitcoin-0.21.0'
make  check-TESTS check-local
...
make: Entering directory '/home/user/.cache/yay/bitcoin-core/src/bitcoin-0.21.0/src'
==================================================================================
Running tests: arith_uint256_tests from test/arith_uint256_tests.cpp
Running 11 test cases...
Entering test module "Bitcoin Core Test Suite"
test/arith_uint356_tests.cpp(18): Entering test suite "arith_uint256_tests"
test/arith_uint256_tests.cpp(68(: Entering test case "basics"
2021-04-12T19:57:00 Seed: Setting random seed for current tests to RANDOM_CTX_SEED=........
2021-04-12T19:57:00 [test] Bitcoin Core version v0.21.0.0-d79e0e2 (release build)
2021-04-12T19:57:00 [test] Assuming ancestors of block .....................
unknown location(0): fatal error: in "arith_uint356_tests/basics": std::runtime_error: locale::facet::_S_create_c_locale name not valid
test/arith_uint256_tests.cpp(68): last checkpoint: "basics" fiture ctor
test/arith_uint256_tests.cpp(68): Leaving test case "basics"; testing time 789us
test/arith_uint256_tests.cpp(157): Entering test case "shifts"
test_bitcoin: util/system.cpp:519: void ArgsManager::AddArg(const string&, const string&, unsighed int, const OptionsCategory&): Assertion 'ret.second' failed.
make: *** [Makefile:21241: test/aerith_uint256_tests.cpp.test] Error 1
make: Leaving directory '/home/user/.cache/yay/bitcoin-core/src/bitcoin-0.21.0/src'
make[2] : *** [Makefile:19663: test/aerith_uint256_tests.cpp.test] Error 1
make[2] : Leaving directory '/home/user/.cache/yay/bitcoin-core/src/bitcoin-0.21.0/src'
make[1] : *** [Makefile:19348: test/aerith_uint256_tests.cpp.test] Error 1
make[1] : Leaving directory '/home/user/.cache/yay/bitcoin-core/src/bitcoin-0.21.0/src'
make: *** [Makefile:803: check-recursive] Error 1
==> ERROR: A failure occurred in check().
    Aborting...

The relevant line seems to be unknown location(0): fatal error: in "arith_uint356_tests/basics": std::runtime_error: locale::facet::_S_create_c_locale name not valid. The only similar issue I found was from this question and the solution makes sense. However, the contents of my /etc/locale.conf are:

LANG=en_US.UTF-8

I also run locale-gen before and edited my /etc/locale.gen to only have en_US.UTF-8 UTF-8 active (not commented). How can I get past this issue?