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=""
```
{
    std::vector<std::string> result;
    for (const util::SettingsValue& value : GetSettingsList(strArg)) {
        result.push_back(value.isFalse() ? "0" : value.isTrue() ? "1" : value.get_str());
    }
    return result;
}
bool ArgsManager::IsArgSet(const std::string& strArg) const
{
    return !GetSetting(strArg).isNull();
}
bool ArgsManager::InitSettings(std::string& error)
{
    if (!GetSettingsPath()) {
        return true; 
    }
    std::vector<std::string> errors;
    if (!ReadSettingsFile(&errors)) {
        error = strprintf("Failed loading settings file:\n%s\n", MakeUnorderedList(errors));
        return false;
    }
    if (!WriteSettingsFile(&errors)) {
        error = strprintf("Failed saving settings file:\n%s\n", MakeUnorderedList(errors));
        return false;
    }
    return true;
}
bool ArgsManager::GetSettingsPath(fs::path* filepath, bool temp) const