If I would write "Boldog, hogy téged boldognak" would have still sense? would that mean "Happy to see you happy"?
Strong and normal:
Boldog vagyok, hogy boldognak látlak.
Stronger and odder:
Boldog vagyok, hogy téged boldognak látlak.
Strongest and oddest, I think it's even incorrect but at least archaic/rural:
Boldog vagyok, hogy tégedet boldognak látlak.
Very strongest and incorrect/archaic+odd+redundant:
Én boldog vagyok, hogy tégedet boldognak látlak.
The personal pronouns in the Hungarian language are optional, but always free to use the personal pronouns and they are always reinforcing the message.
The lazy never said: tégedet. He thinks it is optional, so unnecessary. But his message is not as strong.
I definitely don't think it's the question of laziness.
Moreover, I would think the shorter the sentence the "stronger". (= More expressive.) Alternatively, the longer (= more explicit) the sentence, the "milder" the impression it gives.
But all this doesn't matter if you have to choose for stress or context reasons (/according to your exact message to be conveyed).
Adding "téged" may
- be just more explicit (in a correspondance between two people, where there is no doubt about any third party interference, I would say, there is not much point in it)
- serve to stress "you" (meaning "your happiness - and not anybody else's - is important to me" but then, there has to be some reason...)
- indicate that it may not the same the other way round ("you don't care much about mine...") - and this could also be a candidate (even no.1!) when both personal pronouns appear in the sentence but, of course, context can modify the shades of meaning here, too.
It's not "just like that". It's something that grates on my ears and I think I'm not the only one.Their use may sound superfluous (or heavy) in certain contexts but the use cannot be declared incorrect "just like that".
Yes, it's old-fashioned. I accept hearing that from Petőfi but not in either a formal or an informal conversation or written material today maybe except poetry.("Tégedet" could be a bit old fashioned from time to time ...)
The lack of context is just why it should be emphasized that using "tégedet" is not natural but needs a reason, especially when the OP was posted by a non-native Hungarian speaker. It would be misleading for him to claim that "tégedet" is in everyday use and that it is a perfectly natural way to translate the OP without any special context....we shouldn't just write things off without a context - that we don't have here.