I have logged into Helm after changing the language to Portuguese (or other languages such as Spanish) and I notice that Helm does not display special characters correctly. This means that my users who log in also have this issue.
This varies from browser to browser. However, if you want to set the language to display the same for all browsers, do the following:
[YOUR HELM INSTALL DIRECTORY]\\Helm\\Control Panel\\languages\\YOUR LANGUAGE
and open the language.ini file. Change the LanguageCodeSet to
then save it.
Now go to the following page:
This will load the new codeset into server-side, so it should display correctly for all browsers viewing the control panel.