While testing 17270 I noticed that master (bdda137878904e9401a84e308ac74c93c2ef87c1) does not run on NetBSD. I assume this started after #17085 changed the fallback locale from `C` to `C.UTF-8`. There doesn't seem to be a `C.UTF-8` locale on NetBSD.

```bash
src/bitcoind
terminate called after throwing an instance of 'std::runtime_error'
  what():  locale::facet::_S_create_c_locale name not valid
Abort trap (core dumped)
```

`LC_ALL=C src/bitcoind` works, `LC_ALL=en_US.UTF-8 src/bitcoind` does not.

```bash
locale
LANG=""
LC_CTYPE="en_US.UTF-8"
LC_COLLATE="C"
LC_TIME="C"
LC_NUMERIC="C"
LC_MONETARY="C"
LC_MESSAGES="C"
LC_ALL=""
```
{
    return m_network == CBaseChainParams::MAIN || m_network_only_args.count(arg) == 0;
}
util::SettingsValue ArgsManager::GetSetting(const std::string& arg) const
{
    LOCK(cs_args);
    return util::GetSetting(
        m_settings, m_network, SettingName(arg), !UseDefaultSection(arg),  false);
}
std::vector<util::SettingsValue> ArgsManager::GetSettingsList(const std::string& arg) const
{
    LOCK(cs_args);
    return util::GetSettingsList(m_settings, m_network, SettingName(arg), !UseDefaultSection(arg));
}
void ArgsManager::logArgsPrefix(