So far around 35-37 different nationalities have played for Celtic (depending on what you count as a country, or whether you accept those who played for several national teams). The list below excludes Scottish players as there are too many, and also includes some who never made a first team peformance. It is also incomplete so please do add anyone you spot as missing - most are Irish or English.
AlbaniaRudi Vata 1992-96
Australia
Scott McDonald 2007-
Danny Milosevic 2004
Mark Viduka 1998-2000
Dan Lavery 1948-49
Belgium
Joos Valgaeren 2000-05
Brazil
Juninho Paulista 2004-05
Rafael Scheidt 1999-2000
Bulgaria
Stiliyan Petrov 1999-2006
Cameroon
Jean-Joel Perrier-Doumbe 2007- 2009
Landry N'Guemo 2009 -
CanadaJoe Kennaway 1931-39
China
Du Wei 2005-06
Czech Republic
Jiri Jarosik 2006-2008
Milan Misun 2009 -
DenmarkThomas Gravesen 2006- 2008
Ulrik Laursen 2002-05
Morten Wieghorst 1995-2002
Marc Rieper 1997-2000
Bent Martin 1966
England
Lee Naylor 2006-
Alan Thompson 2000-2007
Chris Sutton 2000-2006
Dion Dublin 2006
Adam Virgo 2005-06
Michael Gray 2003-04 (on loan from Sunderland)
Steve Guppy 2001-2004
Alan Stubbs 1996-2001
Lee Martin 1994-96
Paul Elliot 1989-1994
Carl Muggleton 1993-94
Wayne Biggins 1993-94
Stuart Slater 1992-93
Martin Hayes1990-92
Tony Mowbray 1991-95
Peter Latchford 1975-87
Ben Hutchinson 2008-
Tony WarnerTom Maley 1888-91(born in Portsmouth)
Jim Welford 1897-1900
John 'Jack' Reynolds 1897-98
Ebenezer Owers 1914
John McAlindon 1948-57
Roy Baines 1976-79
Tom Barber 1918
George Elliott 1918
Danny Fox 2009-
France
Stephane Mahe 1997-2001
Stephane Bonnes 1999-2003
Didier Agathe 2000-06
Jeremie Aliadiere 2005 (on loan from Arsenal)
Marc Antoine Fortune 2009 -
Germany
Andreas Hinkel 2008-
Andreas Thom 1995-98
Greece
Georgios Samaras 2008-
Guinea
Dianbobo Balde 2001-
Mo Camara 2005-06
Iceland
Teddy Bjarnasson 2004-08
Johannes Edvaldsson 1975-80
Kjartan Finnbogason 2004 - 2007
India
Mohammed Salim 1936 (never played in the first team)
Ireland (Northern)Patrick McCourt 2008-
Michael McGovern 2001-08
Neil Lennon 2000-07
Allen McKnight 1986-88
Anton Rogan 1986-91
Bertie Peacock 1949-61
Charlie Tully 1948-59
Willie Maley 1888 - 1897
Ireland (Republic)O'Brien, James 2005-
Darren O'Dea 2005-
Aiden McGeady 2004-
Roy Keane 2006
Paul Byrne 1993-95
Packie Bonner 1978-95
Tommy Coyne 1988-93
Tony Cascarino 1991-92
Chris Morris 1987-92
Sean Fallon 1950-58
Peter Kavanagh 1929-32
Patsy Gallacher 1911-26
Colin Healy 1998 - 2003
Pierce O'Leary 1985 - 87
Charlie Gallacher 1959-68
Paddy Turner 1963-64
Mick McCarthy 1987-89
Joe Haverty 1964-65
James Foley 1934-36
Israel
Eyal Berkovic 1999-2001
ItalyMassimo Donati 2007-
Luca Santonocito 2007-
Enrico Annoni 1997-99
Paulo Di Canio 1996-97
Rolando Ugolini 1944-48
Alessandro Sanna 1998-2000Ivory Coast
Olivier Tebily 1999-2002
JamaicaGiles Heron 1951-52
Japan
Koki Mizuno 2008-
Shunsuke Nakamura 2005-2009
MozambiqueJorge Cadete 1996-97 - the first African 'Bhoy'?
NetherlandsJan Venegoor of Hesselink 2006-
Evander Sno 2006
Bobby Petta 1999-2004
Regi Blinker 199-2000
Pierre Van Hooijdonk 1995-97
Glenn Loovens 2008-
New Zealand
Chris Killen 2007-
Micheal McGlinchey 2005 -
NorwayVidar Riseth 1998-2000
Harald Brattbakk 1997-2000
Geir Karlsen (Trialist 1972)
PolandArtur Boruc 2005-
Majiec Zurawski 2005-08
Dariusz Wdowczyk 1989-94
Dariusz Dziekanowski 1989-92
Konrad Kapler 1947-49
Lukasz Zaluska 2009-
Russia
Dmitri Kharine 1999-2002
Senegal
Henri Camara 2005 (on loan from Wolverhampton Wanderers)
Slovakia
Lubomir Moravcik 1998-2002
Stanislav Varga 2003-06
Spain
Javier Sanchez Broto 2003
David Fernandez 2002-03 (on loan from Livingston)
Sweden
Magnus Hedman 2002-05
Henrik Larsson 1997-2004
Johann Mjallby 1998-2004
Switzerland
Stephane Henhoz 2005 (on loan from Liverpool)
Ramon Vega 2000-01 (on loan from Spurs)
USAJohn Blackwood 1899
Dominic Cervi 2009
Venezuela
Fernando de Ornelas 1997
Wales
John Hartson 2001-06
Craig Bellamy 2005 (on loan from Newcastle)
Leigh Roose 1910 - Leigh was tragically killed in WW1