Ever tried that with french?
Example: if you have an ï, it will detect the left dot as single letter. You cannot apply the entire letter to it, because the right dot is the same. So all you could do is assigning the entire letter to everthing which is beneath the dots.
But then, î is misdetected. Last time I tried it I ended up in {\i1}et entraiîne l'Europe dans la guerre.{\i0} and il est de mon devoir d'inviter\nla fille de mon héros à diîner pour.
It really takes some time to fix all that (and why is it mon héros....)

It takes some time to repair SubRip outputs. Really.