Had this one on a new project, building it for the first time:
No steps yet to repro.
After setting the language, this error disappeared.
I find the related legacy code:
cbbLanguage.Items.BeginUpdate;
try
for i := 0 to Languages.Count - 1 do
begin
localeID := Languages.LocaleID[i];
cbbLanguage.AddItem(Languages.Name[i], TObject(localeID));
end;
cbbLanguage.ItemIndex := Languages.IndexOf(SysLocale.DefaultLCID);
finally
cbbLanguage.Items.EndUpdate;
end;
The error should be raised when DefaultLCID is not in the languages.
cbbLanguage.ItemIndex := Languages.IndexOf(SysLocale.DefaultLCID);
needs further investigation.