"There is sugar in the sweet."
Translation:Tá siúcra sa mhilseán.
That's due to lenition rules. Add the 'h' when using a possessive or sometimes descriptive adjective, and the numbers 1-6 I believe.
For example, if I were saying "my sweets" I would say "mo mhilseáin" because I am putting the word after 'my,' which is a possessive adjective. You do the same after namely the word 'sa'
Yes, that's right; san is used when the next word begins with a vowel.
Not sure where you are getting the (i + an) -> sa? I do understand what sa means. You have been very helpful in your answers or comments previous, so in no way am I trying to undermine you just trying to understand. Thank you for taking your time explaining things. I appreciate it. I have actually learned quite a bit from your posts.