It just seemed strange that an ancient race that existed billions of years before the human race would use English.
There are two possibilities.
- The Tardis acts as a universal translator. The words may not have been in English but the Tardis could have been translating them.
However, that doesn't explain the words in the play itself which leads to possibility #2.
According to Tardis Data Core:
Their science was largely implemented using words alone, without much use of instrumentality, suggesting their powers were derived from the lexical equivalent of block transfer (which used pure mathematics to reshape reality).
Based on that, one could conjecture that the words are somewhat immaterial compared to the math involved. The Carrionites could read a grocery list of milk, eggs, bread, cheese, diapers, etc. so long as it added up-so to speak. They were able to use English because the underlying math is more universal.
Given that Shakespeare's words would have been English and his words had such power I assumed that the language does not matter only how its used and applied. I think it would be strange that an ancient language would have power and modern one would not as they are both languages. Unless it was more fantasy than scifi.