How many foreign semi truck manufacturers are there?

Answer 1

All manufacturers are foreign to at least one country. Freightliner, Western Star, and Sterling are all owned by Daimler-Benz. Volvo A.B. is a Swedish company with a North American market, and they also own Mack Trucks. Peterbilt and Kenworth are owned by PACCAR, Inc, and also have production in Mexico and Australia (as does Freightliner).
I don't know exactly how many there are, but I can name the major ones:

• Volvo A.B. (Sweden)
• Scania (Sweden)
• MAN (Germany)
• Iveco (Italy)
• Renault (France)
• DAF (Holland - also owned by PACCAR, Inc.)
• Tata Motors (India)
• Daewoo (Republic of Korea)
• FIRMACO (People's Republic of China)
• Mercedes-Benz (Germany)
• KrAZ (Ukraine)
• Seddon Atkinson (United Kingdom)
• UD/Nissan Diesel (Japan)
• Mitsubishi (Japan)
  

Naming former Soviet companies is a long winded process. Same with Chinese companies - there are probably quite a few, but they'll be marketed under only a couple names for export.
Several marques which may still be found on the road have been taken out of production or folded into other companies. Seddon Atkinson (United Kingdom) is owned by IVECO, and only a very limited number of vehicles with the Seddon Atkinson badge are manufactured. ERF (United Kingdom) was bought out by MAN, who first sold rebadged MAN products under the ERF name in the United Kingdom and South Africa, then eventually removed the marque altogether. Same story with Leyland and Foden (both United Kingdom-based companies), who were bought out by PACCAR, Inc., who ended up taking those marques out of production and replacing them with DAF products.