I think the idea is not to translate user strings, such as the grid cells - people sometimes have extremely large grids, and if the translator would attempt to handle these strings the program certainly will slow down considerably.
With this in the background, I am thinking why the strings of a RadioGroup are not translated?
So, maybe you should file a feature request in the bug tracker to get the strings of the usual containers translated: TRadioGroup, TCheckGroup, TCheckListbox. Not sure about TListbox and TCombobox - the latter at least is ready to accept user input, and TListbox sometimes also contains long lists.