i18n Content Collection with different contents for each language

[karyasuta]

I'm currently building my blog in Indonesian and Japanese (or any 2 different languages for that matter) by using the theme from i18n branch.
My blog will contain posts from both languages and each language has its own posts (no translated posts and different contents).

When trying to write the markdown contents manually (without CMS) and put them in their respective language folder (eg. post/en & post/ja), I notice that it gives me error and only works if both languages share same filenames (I suppose the contents must be translated)
What is the best solution to achieve this?

Thanks for any insights and/or hints