set primary language in preferred languages

Launchpad enables you to choose a list of preferred languages but not to specify which one is your "working-language".

I speak 4 languages, my everyday languages are French and German, my browser languages (as shown in launchpad) are French and English, but for all my Ubuntu and FOSS work I do everything in English only.
So if I could, I would set the "main" preferred language to English in launchpad.
Some people don't speak English, and don't have English as one of their preferred languages, but can have Russian and Polish for instance, how determine which one is the primary one?
Using the country or time zone doesn't work either, the case of Belgium and it's 3 national languages clearly shows why.

this is how I came to ask myself the question:
I am developing an Ubuntu-related website that will use openID. If we use the browser language for the site language, it would most certainly appear, in my case, in French. But I want it to be in English, like launchpad is, like all my FOSS work. So I thought of openID.
The most logical would be to have the site appear in English or the browser language before log-in, but using the main launchpad language associated with the users openID once he's logged in. But this doesn't seem possible for the moment for the reasons explained above.

This would not be a problem if everyone used English, only some people have a very poor level for different reasons, and I want the site to be accessible to *everyone*. Also, it's these little details that make the difference between a very good service and en excellent one. (talking about the planned website)
I'm not sure how this would benefit the normal launchpad user to be honest, as launchpad is only available in English AFAIK, but it seems to make sense to specify which language is the "working" one.