Ways to add a string package of different language at runtime

["Konstantin Aladyshev" <aladyshev22@gmail.com>]

Hello!

I was investigating the possibility of adding localization strings at
runtime. I've noticed that
https://github.com/tianocore/edk2/blob/master/OvmfPkg/PlatformDxe/Platform.uni
has strings only for the `en-US` language. So I've decided to use it
as an example, and create an application that would add translations
for some other supported system language (in this case `fr-FR`):

```
EFI_STATUS
EFIAPI
UefiMain (
  IN EFI_HANDLE        ImageHandle,
  IN EFI_SYSTEM_TABLE  *SystemTable
  )
{
  EFI_STATUS Status;
  EFI_GUID PackageGuid = {0xD9DCC5DF, 0x4007, 0x435E, {0x90, 0x98,
0x89, 0x70, 0x93, 0x55, 0x04, 0xb2 }};
  EFI_HII_HANDLE* Handle = HiiGetHiiHandles(&PackageGuid);
  CHAR16* FrenchStrings[] = {
    L"Configuration de la OVMF plateforme",
    L"Modifier divers paramètres de la plateforme OVMF",
    L"Paramètres OVMF",
    L"Résolution préférée au prochain démarrage",
    ...
    L"2560x1600",
  };
  for (UINTN i=0; i<(sizeof(FrenchStrings)/sizeof(FrenchStrings[0])); i++) {
    EFI_STRING_ID StringId;
    if (i==0) {
      Status = gHiiString->NewString(gHiiString, *Handle, &StringId,
"fr-FR", L"French", L"", NULL);
      Print(L"Added ID=%d, Status = %r\n", StringId, Status);
    }
    StringId = i+2;
    Status = gHiiString->SetString(gHiiString, *Handle, StringId,
"fr-FR", FrenchStrings[i], NULL);
    Print(L"Added ID=%d, Status = %r\n", StringId, Status);
  }

  return EFI_SUCCESS;
}
```

This works well, but I'm a little concerned about the approach that
I've used to initially create the 'fr-FR' string package. Here I've
used:
```
gHiiString->NewString(gHiiString, *Handle, &StringId, "fr-FR",
L"French", L"", NULL);
```
Initially the `en-US` string package has 40 strings, so this code
would create a 'fr-FR' string package with one string of ID=41, which
has a "" value. Because of this hack in the end the 'en-US' package
would have 40 strings and the 'fr-FR' package would have 41 strings.
This is really not a problem of any kind, but maybe there is a library
function to create a string package of a different language?

Best regards,
Konstantin Aladyshev