Random Fact of the Day: Every Tom, Dick, and Harry

Many cultures have generic placeholder names. In American English, we have "Tom, Dick, and Harry" (that is, 'any/all men'), and "John Doe" or "Richard Roe"  (an anonymous/unknown person, although the latter is rather archaic now); while in the UK & Australia there's also "Joe Bloggs" and "John Smith".
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"