Names are spelled the same way, no matter what country you're in, and you should try to pronounce the name the same way the person pronounces his own name.
However, if you're naming a child in Sweden, then you would probably spell it Jonatan, if you want it to be pronounced the Swedish way.
Jonatan is pronounced kind of like you-na-tan, where the a-sound is the same vowel sound as in the word Are.
"Me llamo Johnathan Walker", or "Mi nombre es Johnathan Walker".
¿Cómo están tú y Johnathan?
And is "och" in swedish.
På svenska
"King" in Swedish is "kung".
Equality is "jämlikhet" in Swedish.
School is skola in Swedish.
Adventures is äventyr in Swedish.
29 is tjugonio in Swedish.
Small is liten in Swedish.
Vacation is lov in Swedish.
Celebrate is fira in Swedish.