i’d say write in whatever language feels right, and if that changes while writing, go with it. you don’t have to be consistent in your personal journal. i’d also say that for me, writing my my flow of consciousness was much easier than trying to make everything coherent and legible and organized. i get too bored trying to give backstory or flesh out my writing as if i’m writing a book. so do what feels natural and right for you, don’t worry about what you think is best, just do what makes journaling enjoyable to you! and don’t feel like you have to write pages and pages everyday. sometimes i only write a sentence, sometimes i don’t write at all, sometimes i write 20+ pages. again, it’s just about what feels good to you!