It's a community targeting for non-Japanese to write their entries in Japanese without hesitation. Anybody is welcome to join: somebody who doesn't have any problem writing in Japanese, somebody who is practicing his/her Japanese, somebody who fears that s/he might have forgotten their Japanese, etc. Of course native Japanese's help will be greatly appreciated!
Basically, we'd expect you to write your journal in Japanese. However, if you're not confident on what you wrote, you may write the translation next to it. For comments, feel free to go wild! ... But if you write them in English, it won't help you improve Japanese :/