How can I express the nuance "I 'find' studying Japanese interesting"?
日本語を勉強していることが面白い
Studying Japanese is interesting
日本語を勉強していることが面白いと思う
I think studying Japanese is interesting
The difference in nuance in English is that when you 'find something interesting' it implies you have some experience in the activity. This nuance is not conveyed by the above sentences (in English at least).
日本語を勉強していることが面白い doesn't really mean "studying Japanese is interesting", it sounds like "I find it interesting/odd that he/she is studying Japanese".
"I find studying Japanese interesting" can be expressed as "（私は）日本語を勉強するのが面白い" (or …勉強することが…). If you add …と思う, you can still express the same thing. But it's ambiguous and can also mean "I think it's studying Japanese that is interesting". If you insert な after 面白い, i.e.日本語を勉強するのが面白いなと思う, you can get rid of the ambiguiry and it means "I find studying Japanese interesting/fun".
Studying Japanese is interesting.
You can say it as:
日本語を勉強するのは面白い。
日本語を勉強することは面白い。
I think it'd be more natural to say it as:
日本語の勉強は面白い。
which literally means "Study of Japanese is interesting."
I think studying Japanese is interesting.
So you can say it as:
日本語を勉強することは面白いと思う。
日本語を勉強するのは面白いと思う。
日本語の勉強は面白いと思う。(← I think this is more natural)
