When I want to translate or customize the meaning of a word directly from the dictionary, some languages don't appear. The same happens with notes.
For example, while I can't add an Italian note, I can customize the meaning of a word in Italian, and the same goes for Arabic. Vice versa, I can add a note in Portuguese but that language is not selectable when trying to customize the meaning of a word.
This isn't a bug as much as a shortcoming in how renshuu handles languages - multiple languages for all of these options were not in renshuu many years ago, and so the system for which languages to show where is scattered.
It *is* something I hope to fix in the future, but not at the moment.