I would recommend a learning journal for an entirely different reason: self analysis. Keeping solid documentation of your learning allows you to witness actual progress from "when I was a beginner" to "now", see how you may have had misconceptions about a particular issue in the language (which makes it easier to identify and teach about to other learners), and allows you to identify "pain points" that you've been stuck on without progress so you can work on them!

None of this freedom of creativity mumbo jumbo (something readily available in a language without a journal).

In your About Me you don't mention which language you learned. I imagine it's Japanese based on this blog, but that may not be obvious to people reading the page. Also, while some would say "Japanese is the hardest language in the world" (due to "3 alphabets") I would argue Chinese is harder (tones are a lot more difficult!), and many tribal African languages far more difficult.

ps.

I bought a pocket-sized Moleskine (or maybe similar journal?) nearly 5 years ago - it's unmarked and unbranded and I was never able to find it in a store again. So thank you for introducing me to the brand-name of this fantastic journal. I absolutely love how it's lasted the test of time.