Building (and maintaining) a multi-language website has always required back-end access and most likely the use of Joomfish (in J1.5). Joomla 1.6/7/8 brings a big change, also for how you can use F2C.
Joomla 1.5 (Joomfish) multi-language websites & F2C
Since F2C creates Joomla articles it is 100% compatible with JoomFish. This means that a Joomla article created using F2C is no different than an article created using the Joomla Article Manager. As a result the articles can be 'imported' and translated using JoomFish.
PLEASE NOTE: If you have your F2C articles translated using JoomFish and you where to change the content of the article you would need to update your translations using JoomFish. This works just like Joomla native articles.
Can F2C also create Joomfish translations?
The answer is NO, F2C cannot create the translations and submit them to the Joomfish DB.
Joomla 1.6/7/8 multi-language websites & F2C
In the latest Joomla version multi-language content is supported. This means that you CAN USE Form2Content to create multi-language content.
1) Create different (nested) categories for you content per language.
2) Create a copy of your F2C submission form and F2C template PER language (i.e., several F2C Content Types)
3) Link each F2C content type to the correct Joomla categories for saving the articles
4) Make sure you have language settings set correctly.
WE DO NOT RECOMMEND YOU USE ONE F2C CONTENT TYPE FOR CREATING ARTICLES IN DIFFERENT LANGUAGES