Mail messes up html emails when the international panel set to "french"

Question

This is a fairly specific problem, under my normal settings everything works fine. I receive emails on a weekly basis from this sender who sends them with quite a bit of html encoding. Images, fancy formatting, tables, etc. Normally, they display just fine.
However, I recently decided to switch my system language (on the international panel) to french instead of English. I have not changed any other settings, in the system or in Mail.
With the setting in the international panel set with French first, mail suddenly displays these emails suddenly turn to gibberish: They lose almost all formatting, most of the images disappear, text gets superimposed and piled up near the top of the email, etc.
Thus my two questions: Firstly, why would the setting in the international panel be affecting the content of an html email. Secondly, how can it be set to not affect said content.
I already looked through the coding for the email, and to the best I can tell, it has no encoding specifying a display language or alternate language encoding or anything of that sort.
Thanks!

Answer 1

With the setting in the international panel set with French first, mail suddenly displays these emails suddenly turn to gibberish: They lose almost all formatting, most of the images disappear, text gets superimposed and piled up near the top of the email, etc.
Hmmm, I'd copy that text & paste into Text Edit document, then wirth it all highlighted try changing to several different fonts to see if the gibberish goes away.
I'm thinking it's a font issue, but not certain of course.
Maybe post a sample of the gibberish here for me to look at?