As of today, building localized Domino/Notes applications is a painful experience. I've seen dozens of approaches invented by creative Notes developers, trying to overcome the lack of built-in localization support in Designer. However, none of these comes even close to the features and ease of use of modern development tools with regard to localization.
P.S.: I do know that Domino Global Workbench exists, and I've been using it for years. But let's face it, DGW is cumbersome to handle, it has many limitations, and it produces inefficient code.