I know that SocialEngine stores language files as CSV files in application/languages. The common format in the CSV files is as follows:
"Source word"; "Translated word"
But, this sometimes gets very complicated, especially when special characters are used in some parts, e.g.:
"Total Credits : %s";"Total Credits : %s"
"_EMAIL_SITEGROUP_BADGEREQUEST_APPROVED_EMAIL_TITLE";"Group Badge Request Approved"
"Video conversion failed. Please try uploading %1$sagain%2$s.";"Video conversion failed. Please try uploading %1$sagain%2$s."
"{item:$subject} replied to a comment on {item:$owner}\'\'s page offer {item:$object:$title}: {body:$body}";"{item:$subject} replied to a comment on {item:$owner}\'\'s page offer {item:$object:$title}: {body:$body}"
"3%s Level Category:";"3%s Level Category:"
"I have read and agree to the <a href='javascript:void(0);' onclick=window.open('%s','mywindow','width=500,height=500')>terms of service</a>.";"I have read and agree to the <a href='javascript:void(0);' onclick=window.open('%s','mywindow','width=500,height=500')>terms of service</a>."
Without worrying about any of that, you can use this plugin: Language Translator / Multilingual Plugin