Warn before deleting a translation

[martin-trummer]

When we have an existing translation for a key, e.g. xxx and then add a new translation with a subkey, e.g. xxx.child, then the existing translation xxx will be deleted silently and instead we now have only the new info, which is an object xxx with one property child

it would be great if the plugin could show a warning before overwriting and maybe even offer to move the existing translation to a new child property.