I installed Mint 11 a couple of days ago and this morning I was faced with the same problem I had with Ubuntu 10.04.
Upon installation I went to language support and added Greek language as a second language. My language listings in the language support is:
English USA first
English Canada second and
Greek modern third with
English fourth and last to deactivate other languages below.
After done the selection I clicked the button "Use system wide" and proceeded to add a Greek keyboard which was automatically placed in the panel and works fine
All was fine for a couple of days. This morning I noticed that most of my menus turned out to be Greek. I do speak and write Greek so this is not a serious problem for me, but it is highly unusual. Not all menus are now Greek, The main menus at the top (Applications, Places and System) are Greek, most of their contents are also Greek. Inside the individual menus, such as office, very few are Greek and so on.
What I would prefer is to have English as the only system language and Greek as a second language.
I had the same problem in one Ubuntu 10.04 and in my desperation I went to language support and deleted completely from language support the Greek language and kept the keyboard to dual language. I was worried that spell checkers etc will disappear for Greek, but they did not. There are still a few Greek heading here and there, but very minimum.
As I said I can live with this problem, but it simply bothers me and other users with second languages may have their problems too. There must be an explanation and hopefully a solution. I will try removing the Greek language and report back here if it works.
Same day at 8:40 AM update
I did remove the Greek language, then opened a LibreOffice Writer and typed some Greek with no problems and all intentional errors were found and corrected. So now all is fine again. But there was another problem that appeared when I tried to do restart in order for changes to appear. Upon clicking restart, screen went blank and nothing happened for a few minutes. I had no choice but to force close the computer, wait a couple of minutes and start again. I have the hunch that this is not due to my computer, but it is rather a bug and I have the hunch that I read something about it under Mint.
Anyway for now all systems are working.