Count the number of glyphs in a text layer

Hi guys. I really hope someone can shed some light on this problem.

I am working with some arabic texts and I want to highlight words based on their position. I can count from end to start in order to reverse the animator but the thing is that JavaScript and after effects animator count the characters in a different way. So JavaScript .indexof() function does not count the characters in the same way that the animator range does.

Ex: if I use “لى” as text source, animator says it is 1 character while text.sourceText.length (of which count is similar to .indexof()) says it is 2. If I have one of two of this in my string, the whole thing works badly. Is there any way to either make the animator count this as 2 or make JS see it as one?

As a side information, I noticed that animator does the same thing for “fi” or other ligature in the fonts that have them. If your font has the “fi” ligature, AE counts it as one char. But activating or deactivating ligatures has no effect in the arabic text layer.