I'm in Indonesia rn and I can confirmed at least the Indonesian one is true. "Datang bulan" (literally "Moon comes") is the more formal way to say that someone has their period. But most Indonesians speak slang here which is just "Dapet" ("Get") so someone usually says "Aku/gue lagi dapet" ("I'm getting [it] right now"). Guessing it started as a code but now everyone knows and just roll with it.