Multilingual forms without Joomla language selection

At first: Sorry for my bad English!
I want to embed multilingual forms in an "iframe" on a Webserver where no Joomla runs.
In version 3.1 it was possible to "install the translation using:
[en]Bank:[/en][fr]Banque:[/fr][it]banca:[/it] in the code.
With the language code at the beginning of the form:
<?php $_SESSION [Mylang code]="en";?>
you could call the appropriate language version.
How i can now create Chronoforms6 multilingual forms without the user choosing the language, i.e. i want to call the language xxxx directly in an IFRAME, e.g.:
<iframe src="http://xxxxx/index.php?option=com_chronoforms6chronoform=contact&tmpl=component"></iframe

Thanks for any help, tips, etc.
Leo

Hi Max
We are a foundation, i.e. a non-profit organization, so the site also runs on a outdated SharePoint platform (SharePoint 2007). Unfortunately, we lack money for the individual development of the forms with SharePoint. That's wha i decided years ago for Chronoforms and i am very happy so far. Now we should definitely bring Joomla server to a current version, so i have to do now neverything new with Chronoforms 6.
In SharePoint, i use a WebPart and added the link in a iframe.
You can find the forms (chronoform 3.x) here:
http://www.ibcsg.org/Pages/Contact.aspx
http://www.ibcsg.org/SupportUs/en/Contact_Donations/Pages/ContactForm.aspx
http://www.ibcsg.org/SupportUs/fr/Contact_Soutien/Pages/Formulairedecontact.aspx
http://www.ibcsg.org/SupportUs/it/Contatto_aiutare/Pagine/ContactForm.aspx

Best regards,
Leo
http://www.ibcsg.org/SupportUs/de/Kontakt_Spenden/Seiten/ContactForm.aspx

Hi Max

Thanks for your answer (input)! Forget everything that i wrote. I'm pretty inexperienced with Joomla 3.x and the multilingalism.
But your input about "just pass the language code in the URL" was just the right thin. After i set Joomla correctly on multilingualism, i was able to solve my problem with language code in the URL. Thank you ver much and have a nice Day!

Best regards,
Leo