I updated existing ISM to a accommodate localization changes.
I am installing resource dlls in respective language folder.
Name of dlls and number of dll are same in language folders.
That is “en” folder contain test.dll (containing English resource) and “fr” folder is also contains test.dll (containing French resource).

Here after installation (setup prepared using install shield 12.0 )it replaces test.dll from “fr “folder to “en” folder. And all folder contains same DLL.