I'm pretty convinced Black Suit was the one behind all of this, knowing how manipulative and cunning he is, he pretty much predicted sensei's answer and the students' reactions. If this gets further out of hand, sensei will definitely have no choice but to join Gematria.
All the juicy info are already explained, I'm just gonna add the terms for this specific case:
Standard (baku), formal, informal, colloquial (not sure which one is first here: spoken or colloquial, maybe interchangable?), slang.
Indonesian is in a state of diglossia so, at the very least, one needs to know two forms of the register to understand formal Indonesian in academic settings, and daily life.
I know the term first from Langfocus. Note: not all the terms exist yet in KBBI, some exist in wiktionary, until a requests are sent for more forms.
these arent really registers that would be Japanese's, Javanese's, etc. I guess varieties kind of like Vulgar vs Classical Latin divide. or tldr going by wikipedia for now L:low variety, vernacular language and H:High variety, a second highly codified lect. I guess multi-glossia is good enough for draft?
The multi part is the extended forms: also include regional Indonesian accent with different vocabs using code mixing with the regional languages of the area.
That ends there, since it would be a different languages if it goes further.
Javanese Arekan dialect continuum is for 1 language. Since Indonesian itself is the H language and standard, most regional languages are being used as L variety only in cities, and mostly used as H variety when talking to elders in the case of register of Javanese.
Also why it's hard to maintain fluent Javanese register vocab for example, I applaud the abdi dalem or guide that tell visitors to the keraton in Javanese register highest variety. source of this last sentence by Londokampung krama inggil video in YT (it's a joking video, but it's a great way to teach and preserve the register so the speakers don't decline).
(I only take one example of a regional language in Indonesia that has a register, there are list of this if you search it hard enough, in forums, or wiktionary DC. because of my lack of info, I can't give a general list of all the regional languages in Indonesia that have register, and other kind of terms here like diglossia, and dialect continuum)
