I have read this question: How to set the default language for customers, suppliers?

But in my case, I use english as my default language and my assistant uses spanish as hers. 90% of our customers have spanish as their default however when I try to send an email, print a quote, order, invoice, etc they come out in english even though the language for the customer is spanish. When my assistant does the same they come out in spanish.

It is apparent that the system is choosing the user language over the customer language. Is this the correct behavior? If not, how can I correct it?

Regards