Does this make sense and what does it mean?
そのあとで、日本語がとくいだことになったと思います。
Does this translate to: After that I think I became good at Japanese?
Does this make sense and what does it mean?
そのあとで、日本語がとくいだことになったと思います。
Does this translate to: After that I think I became good at Japanese?
You could say:
日本語が得意になったと思います。
ことになる has a different meaning. According to "A Dictionary of Basic Japanese Grammar", page 202: "An event takes place as if spontaneously, irrespective of the speaker's volition."
No. If it's 日本語が得意{とくい}なことになった, it means "I ended up being regarded to be good at Japanese (against truth)", though.