I'm kinda confused on what you expect out of CentOS that Windows provides? Or is that you know Windows can't provide it but hoping CentOS can?
Windows has what is called a "Global IME". I'm not sure what "IME" stands for or how it works, but I can tell you what it does for me, the end user.
In Windows, I have a small panel called the "Language Bar", which you can place anywhere, but I have it on the bottom of the screen, just to the left of where my system tray and time display are. It's basically a little blue square icon that has the letters "En" on it. By clicking on this button, a pop up menu appears, which in my case gives me three choices: English (US), English (Canada), and Japanese.
In supported applications, which these days is almost everything, I can set the Language Bar to Japanese, and then I can input Japanese straight into the program. Not only does this work for Microsoft products like Office, but most every other program built within the last couple years. Significantly, I can input Japanese directly with Adobe Illustrator and Photoshop.
Even more significanly, I can use this input method for programs, in Windows, like OpenOffice, Firefox, and Thunderbird. This is why I more or less assumed Linux would be able to as well, because the applications that I also use in CentOS support the feature in Windows.
As for the keyboards, again, I don't know how it works, but I just type in Japanese phonetically, the same way it works on a Japanese keyboard, but still using my US English keyboard. In fact, I prefer to use my US English keyboard for typing Japanese because Japanese keyboards have a tiny space bar that I'm always missing and hitting other keys, and they weirdly map thigs like an apostraphe to being above the seven and other odd choices. With Windows, my keyboard retains its mapping, but the result is that I can type in Japanese characters.
It's this functionality which I assumed CentOS was offering with it's "Input Method Switcher". After all, the Input method switcher does sit on my top panel with a little white squre icon with "En" on it, just like Microsoft's Global IME. If the "Input method switcher" does not allow me to type in other languages, then what does it do?
Dave