this is not fully supported yet. I have half-cooked patch on my laptop that improves the stash sharing and acceptance workflow but I have not managed to finish it .
Currently the only way is to re-apply the shared stash and rebase it. If there are no staged strings after the rebase, it means that all stashed strings were included into the pack. If some string is still staged after the rebase, it is different from what is in the lang pack.