I am very glad and joyful as you joined in my birthday celebration. I am writing this letter to thank you for giving me such a beautiful birthday present. I always wanted to have that kind of watch. You fulfilled my dream uncle. I love the wonderful smart watch. It's much appreciated uncle. Thank you.
Colloquial speech refers to language that is common to a specific area or group. In this case, it's not proper English to say "gonna", but everyone understands it to be the combination of "going to"