How to get custom field labels translated
Last days, I got the same issue to translate labels and descriptions of custom. here is what i did to solve it.


Enable i18n's i18_field "Field translation" submodule
Go to admin/config/regional/translate/i18n_string
Checked 'fields' (properly check all) and Click on "Refresh strings".
Go to admin/config/regional/translate/translate
Search desired string and translated it to other lang.