Thanks very much for your reply. Meanwhile I had also asked an Indonesian friend of mine (since it took quite some time to get a reply here
) and she said, besides your suggestion, one could also say
'Saya membaca suratmu yang mana kamu bercerita (...)'
I keep having difficulties with relative clauses. I've got quite a thick Indonesian grammar reference, but it has far too few examples about this. I thought about another such sentence the other day:
'the company I work for' => normally you could say 'perusahaan tempat saya bekerja', but I work as a free-lance translator for them at home, so I don't literally go there. Any suggestions? I don't think I can make a construction like 'untuk mana'?