First: You have to create an empty po file for your module.
Under Settings ---> Translations ---> Click on Export Translation
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Open the downloaded PO file (your_module_name.po) with POEdit, translate it, and save it as: ar_xx.po where xx = country code (as follow):
ar-DZ Arabic - Algeria 0x1401 ARG
ar-BH Arabic - Bahrain 0x3C01 ARH
ar-EG Arabic - Egypt 0x0C01 ARE
ar-IQ Arabic - Iraq 0x0801 ARI
ar-JO Arabic - Jordan 0x2C01 ARJ
ar-KW Arabic - Kuwait 0x3401 ARK
ar-LB Arabic - Lebanon 0x3001 ARB
ar-LY Arabic - Libya 0x1001 ARL
ar-MA Arabic - Morocco 0x1801 ARM
ar-OM Arabic - Oman 0x2001 ARO
ar-QA Arabic - Qatar 0x4001 ARQ
ar-SA Arabic - Saudi Arabia 0x0401 ARA
ar-SY Arabic - Syria 0x2801 ARS
ar-TN Arabic - Tunisia 0x1C01 ART
ar-AE Arabic - United Arab Emirates 0x3801 ARU
ar-YE Arabic - Yemen 0x2401 ARY
Under your module folder create a subfolder and name it i18n, copy your ar_xx.po file in this folder.
Click on Import Translation and import your ar_xx file
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Last, under Settings ---> Translations ---> Application Terms click on Synchronize Terms
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An example of translated term in POEdit:
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Some useful links:
OpenERP
ISO_639