Tbh, His/Her response to the golem is actually creative. Magic is usually overly exaggerated in a lot of cases or very extravagant and some simplicity shows creativity imo.
@ SunSun I think even with their normal language, the handwriting argument can be applied. I don't think the ancient language is necessary if that were the case.
But like @ SakuraShower said, if you practice the language often enough, you can easily recognize what is being written. So, I really don't understand why they're all learning the same language. Someone/some people is/are bound to become more proficient in that language and therefore be able to read other people's attacks (especially if we don't consider the handwriting argument and only taking into consideration that they are STILL battling the notion that other people know the language). There's no difference between speaking one language that people use every day versus casting spells with a language that everyone knows.
It could also be as someone else said that it's more to do with 'intention'... in which case...
Maybe they should all just create their own language. Lol