If you are asking if the sentence is grammatical: Yes, it is grammatical.
If you are asking if the sentence makes sense: Yes, it makes sense.
However, if you are asking if there is a better word than "similar" to use in this sentence: Possibly, but it doesn't really make much difference. I might have said something like:
The sound of the word should mirror its form.
For me the real issue is that I don't really like either "sound" or "form" in this sentence, as the more precise terms "pronunciation" and "text" would seem to be a better fit. Again, it makes little difference in context, as I understand completely what the author is saying.
I'm guessing the eventual point of this passage is that English, sadly, does not follow this rule. Not by a long shot.