For some languages, the 'names' aren't actual names you'll find on people; rather, they literally just mean "anonymous" or "whoever"; but others are (or were) in general usage [indicated by bold].
Arabic:
- "Fulan" --- "whoever"
- "Fulan bin Fulan" --- "whoever, son of whoever"
Bulgarian:
- "Petar Petrov"
Chinese:
- "Zhang San", "Li Si", "Wang Wu" -- "Zhang Three", "Li Four", "Wang Five" [Zhang, Li, & Wang are surnames]
- "Wang Xiaoming", "Chen Xiaoming", "Chen Tai Man"
Danish:
- "Morten Menigmand" -- "Morten Ordinary-man"
Dutch:
- "Jan Jansen"
Finnish:
- "Matti & Maija Meikäläinen" -- "Matti & Maija One-of-us"
French:
- "Jean Dupont"
- "Pierre, Paul, & Jacques"
German:
- "Hinz & Kunz"/ "Heinrich & Konrad"
- "Lieschen Müller"
- "Max & Erika Mustermann" --- "Max and Erika Sample-man"
- "Otto Normalverbraucher" --- "Otto Average-consumer"
Hebrew:
- "Ploni", "Ploni Almoni" -- poss. "indicated", "indicated hidden"; a Biblical placeholder name
Hungarian:
- "Minta János" -- "John Sample"
Irish:
- "Seán Ó Rudaí" -- "Sean O'Things"
Italian:
- "Tizio, Caio, e Sempronio" -- modern Italian version of Roman placeholders (Titus, Caius, & Sempronius)
Japanese:
- "Daredare" -- "whoever"
Lithuanian:
- "Jonas Jonaitis", "Petras Petraitis"
- "Vardenis Pavardenis" (m) / "Vardenė Pavardenė" (f) -- "Name Surname"
Norwegian:
- "Ola & Kari Nordmann" --- "Ola & Kari Norwegian"
Persian:
- "Fulan" -- "whoever"
- "Bahman" --- "whoever"
- "Fulan o Bahman" --- "whoever and whoever"
Polish:
- "Jan Kowalski" / "Janina Kowalska"
- "Jan Novak"
Portuguese:
- "Fulano" -- "whoever"
- "Fulano, Sicrano e Beltrano" / "Fulana, Sicrana e Beltrana" -- "whoever, _____, & Beltrano" [origin of Sicrano is unknown; Beltrano is a surname]
Russian:
- "Imyarek" -- "name"
- "Ivan Ivanovich Ivanov", "Pyotr Petrovich Petrov", "Sidor Sidorovich Sidorov" -- sometimes mix-and-match
Serbian:
- "Pera Perić"
Slovak:
- "Janko Mrkvička", "Jožko Mrkvička" -- "Johnny Carrot", "Joey Carrot"
Spanish:
- "Fulano" / "Fulanita" -- "whoever"
- "Fulano, Mengano, y Zutano" -- "whoever, whoever, & _____?" [poss. related to Latin scire "to know"]
- "Juan Perez" [Latin America]
Swedish:
- "Medelsvensson" -- "average Svensson"