Having all the dialog logic in a single switch statement doesn't mean that all the text is right in there. It can still be referring to IDs which are then looked up in a table for the right translation.
That would still be a step above the Undertale case, where the dialog was in the code. The big problem there is that your localisers now need your source code and (potentially expensive commercial) build system to test that their script doesn’t break anything. Or you end up in an expensive back-and-forth with a contractor compiling it for them.
Just taking localisation strings out of the switch statement doesn’t fully fix this. You can swap out individual lines, but characters are still bound to say the same number of lines in the same order in every language, with player choice happening at the same point. This may work for simple conversations, but it will result in clunky localisations when languages differ in verbosity or sentence structure.
