How to translate inline entity form nodes (or, product variations in kickstart)
I'm not 100% sure on the setup, but I just finished a site that dealt with a similar circumstance. It uses String Overrides to perform targeted text changes, and if it doesn't support Internationalization by default then there's a module that provides additional tabs at /admin/config/regional/stringoverrides for each enabled language.

For reference, here's the translation module list currently enabled on the site:

Locale
String Overrides
Entity Translation
Entity Translation Upgrade
Block languages
Contact translation
Field translation 
Internationalization
Menu Translation
Multilingual content
Rules Translation
Synchronize Translations
Translation Sets
Views Translation
Variable


Not all of these modules are required to make this happen, but perhaps you can compare your own setup to this list and find some differences. Apologies for not remembering how to set this up.

UPDATE :: Process for enabling translation within String Overrides

== Modules ==


Internationalization :: link | download
String Overrides :: link | download
Variable :: link | download


Enable Modules:


Locale
Variable
Internationalization
String Overrides
String Translation

Add a new language


/admin/config/regional/language/add
Select, click "Add language"

Add translations for alt language strings


/admin/config/regional/stringoverrides, click desired language in top right
Add rows for each desired string, place original language text in left box and translated string in right box
Save, view on front end




The final interface should look something like the following cap: