Assalamualykum.
Brother some anti-Islamists like to claim that adding vowel mark has changed the Quran. Besides they claim that a language undergoes changes with the change of time. They ask, how did how did Hajjaj Bin Yusuf who came many many years after Muhammad (SAW), Hazrat Abu Bakr, Hazrat Umar, Hazrat Uthman and Hazrat Ali ,know where to put the vowel marks? They say at first Quran didn't make any sense, so to give it a meaning the early Muslims added vowel marks. Below are their claims:
1. A simple definition of language is. How we communicate information to others.
2. Eternal medium for this transfer of information is by sound symbols. This is called speech.
3. Since, sound dies as soon as it is uttered from speakers. It could not be preserved until modern times, unless it was preserved in the form of script. Hence, Language, meanings and script are very interdependent.
4. Furthermore, languages change overtime. All aspect of language that is, Lexical (meanings/concepts associated with words), grammar, phonology, semantics and syntax, all of these.
5. Hence, in the face of changing landscape, preservation in the form of script is/was very important and related.
They say that the vowel marks can be put anywhere according to its necessity to give a word a meaning.
So, How do we answer these anti-Islamists to shut their mouth once and for all?