Please note: I speak pidgin Irish, no Romany, no Arabic. I may very well have screwed up any of the below.
Arabic
abu: 'uncle.' Used as slang term for an older man.
ad Da'ud: Ibrahim 'Abd ar-Rahman ad-Da'ud, Republican Guard leader named minister of defense after the 1968 coup, presumed anti-Ba'athist and exiled to Jordan in 1968.
al salaam a'alaykum: 'peace be upon you.'
argilah: pipe.
Ba'athists: The briefest definition ever: Saddam Hussein's political party in Iraq.
bel salaam: 'peace.' Greeting.
bismillah: 'in the name of God.'
ghusl: full ablution in Islam. I had Sayid follow Sunni practice.
hadith: folk tradition in all branches of Islam, with varying beliefs amongst the traditions.
hajj: Muslim pilgrimage to Mecca.
hijab: Muslim modest dress.
ihtaris - al-Jarrah ilhadun wa zindiqun: 'beware - Jarrah is a heretic and an atheist' (had someone check out the Arabic on this, but if I have it wrong, please feel free to correct me.)
Isa: 'Jesus.'
jahsh: 'dumbass,' but not quite as harsh.
mahdi: Islamic messiah.
Qa, 'alif, dal, ya, ra: Q-A-D-I-R.
sadikie: 'pal.' Informal.
salaam: 'peace.' Non-literally, a style of bowing.
shahadah: pronunciation of faith in Islam, or Islamic creed (Sayid recites it in 'Solitary' when Danielle traps him.)
shamal: A particularly bad type of desert wind.
Sidi Mohammed: Muslim ruler of Morocco in the mid-1850s, famed for an impressive court.
sukran: 'thank you.'
takbir, tahmid, tahlil, and tasbih: Muslim recitative prayer, obligatory.
ya 'Ammo: Informal title of respect to someone a generation older or younger.
ya Bek: Formal title of respect used for police and military officers.
ya Doctor: 'Doctor,' 'Professor,' etc. General formal academic title.
ya Sidi: General title of respect. Formal title for police and politicians, not used in official communications.
yalla: 'let's go.' Informal.
Irish (Gaelic)
mo chara, nár lagaí Dia do lámh: 'my friend, may God not weaken your hand.'
Sassenach: Saxon (English).
siúl: 'walk' (declarative.)
slán agat: 'safe by you.' Non-literal 'goodbye' (by the leaving person).
slán leat: 'safe with you.' Non-literal 'goodbye' (by the person who is left).
Other Languages
ja wohl: 'yes!' (emphatic.) German.
kafes: 'cage.' Turkish.
kala azar: 'black fever.' Hindi. (Leishmania donovani.) Parasitic disease of the internal organs spread by sandflies.
punji sticks: camouflaged stakes tipped with poison or worse.
spiuni baro: 'spy man.' Romany, the Rom (aka Rroma or "gypsy") language.