From Facebook Developer Wiki

The following locales are all live and translated on Facebook. The basic format is ll_CC, where ll is a two-letter language code, and CC is a two-letter country code. For instance, 'en_US' represents US English.

The locales generally follow ISO language and country codes specified in ISO 639 and ISO 3166 respectively, concatenated by an underscore. Note there are two exceptions that may not quite follow the ISO standard- ar_AR and es_LA. We use these to denote umbrella locales for Arabic and Spanish, despite in the latter case having a few more specialized localizations of Spanish.

You can determine this information about a user by calling users.getInfo or querying the user FQL table.

Locale

Language

af_ZA

Afrikaans - Afrikaans

sq_AL

Albanian - BETA - Shqip

ar_AR

Arabic - العربية

az_AZ

Azeri - azərbaycan dili

eu_ES

Basque - BETA - Euskara

bn_IN

Bengali - বাংলা

bs_BA

Bosnian - BETA - Bosanski

bg_BG

Bulgarian - Български

ca_ES

Catalan - Català

zh_HK

Chinese (Hong Kong) - 中文(香港)

zh_CN

Chinese (Simplified) - 中文(简体)

zh_TW

Chinese (Taiwan) - 中文(台灣)

hr_HR

Croatian - Hrvatski

cs_CZ

Czech - Čeština

kw_GB

Cornish - Kernewek

da_DK

Danish - Dansk

nl_NL

Dutch - Nederlands

en_PI

English (Pirate) - BETA - English (Pirate)

en_GB

English (UK) - English (UK)

en_US

English (US) - English (US)

eo_EO

Esperanto - BETA - Esperanto

et_EE

Estonian - BETA - Eesti

fo_FO

Faroese - Føroyskt

tl_PH

Filipino - Filipino

fi_FI

Finnish - Suomi

fr_CA

French (Canada) - Français (Canada)

fr_FR

French (France) - Français (France)

gl_ES

Galician - BETA - Galego

ka_GE

Georgian - ქართული

de_DE

German - Deutsch

el_GR

Greek - Ελληνικά

he_IL

Hebrew - עברית

hi_IN

Hindi - हिन्दी

hu_HU

Hungarian - Magyar

is_IS

Icelandic - BETA - Íslenska

id_ID

Indonesian - Bahasa Indonesia

ga_IE

Irish - BETA - Gaeilge

it_IT

Italian - Italiano

ja_JP

Japanese - 日本語

ko_KR

Korean - 한국어

la_VA

Latin - BETA - lingua latina

lv_LV

Latvian - BETA - Latviešu

lt_LT

Lithuanian - Lietuvių

mk_MK

Macedonian - BETA - Македонски

ms_MY

Malay - Bahasa Melayu

ml_IN

Malayalam - മലയാളം

ne_NP

Nepali - नेपाली

nb_NO

Norwegian (bokmal) - Norsk (bokmål)

nn_NO

Norwegian (nynorsk) - BETA - Norsk (nynorsk)

fa_IR

Persian - BETA - فارسی

pl_PL

Polish - Polski

pt_BR

Portuguese (Brazil) - Português (Brasil)

pt_PT

Portuguese (Portugal) - Português (Portugal)

pa_IN

Punjabi - ਪੰਜਾਬੀ

ro_RO

Romanian - Română

ru_RU

Russian - Русский

sr_RS

Serbian - Српски

sk_SK

Slovak - Slovenčina

sl_SI

Slovenian - Slovenščina

es_LA

Spanish - Español

es_ES

Spanish (Spain) - Español (España)

sw_KE

Swahili - BETA - Kiswahili

sv_SE

Swedish - Svenska

ta_IN

Tamil - தமிழ்

te_IN

Telugu - తెలుగు

th_TH

Thai - ภาษาไทย

tr_TR

Turkish - Türkçe

uk_UA

Ukrainian - BETA - Українська

vi_VN

Vietnamese - Tiếng Việt

cy_GB

Welsh - Cymraeg