"Du bist ein schöner Mann."(informal) "Sie sind ein schöner Mann."(formal) But I think, you would rather say "Du bist schön." That should do. In most cases, it will sound unusual to a German to hear a sentence like the very first one.
But otherwise, that's the word by word translation.
beautiful boy = schöner Junge
To say he is beautiful in German you would say er ist schön. If you wanted to say she is beautiful, you would say sie ist schön. Sie sind schön means they are beautiful.
beautiful in German = schon (the 'o' has two dots over it)
For a boy, you would say "allemand" and for a girl, you would say "allemande" in French.
schönsten
hübsche Cousine is the translation in German. It is translated from English to German. German is mostly spoken in the European countries.
Junge.
English: "the boy" means in German: "der Junge" or "der Knabe".
Huebsche Frau
Sie ist wunderschön.
You have beautiful eyes - Du hast schöne Augen.
"Junge" would be the correct way to say "boy" auf Deutsch.
Deutschland war schön.