Sorry for the delay to respond.
Looking at your screenshot, you installed the English US version of Iron (while I installed the French one) so it is normal that Iron primary language is English US for displaying and spell checking.
As for English, which seems to me to be British English, it is the same result as yours on my side. I assume that when we installed Iron we did not add British English components. I know for sure that I did not on my side.
For the French choices now. You cannot display Iron in French because you installed the English US version, but, if at the installation you also selected French as a second language you should be able to spell check in French too.
SEARCH ENGINE: Try using a France search engine.
Go here http://www.google.fr/
and do a simple search. Then go to Iron settings - Search - Manage seach engines.
Because you already did a search, the France search engine will be added in the options. Click on it to highlight it and select "Use as default"
I hope this is not clear as mud...
I too have a question: If you want everything in French why do you install the English version, which is by default English US ? Why not install in French from the beginning ?