Im german, lets see if i can help. Do they want to get married on her visit or just live together?!
If she only wants to visit him she may apply for a Visitor visa(Besuchervisum). With that she can stay up to 3 months, but it can be extended. An Invitation or Verpflichtungserklärung is needed in indonesia to get the visa(or she has proof that she has enough money to pay on her own).
To get the Verpflichtungserklärung he needs to go to the lokal Amt für Ausländerangelegenheiten.He needs her adressn name, birthdate and passport number, it then will take maybe a week n costs 25€.
He has to send this Document to her an she can apply for a visa at the german embassy in jakarta(1 week) or a consulat in medan or surabaya(3 weeks). She needs whats written on this page www.deutschebotschaft-jakarta.(...)isa/visatourist.html
To marry in germany they need a special visa which means a lot more paperwork. Im not that far yet :p
For that u need to apply for longtime visa.
Marrying without the proper visa is forbidden in germany. But u can trick them and marry in Danmark or other European countries. He then needs to apply for Familienzusammenführung which will lead to a permanent visa for her.