Can you list the contents of your /mnt/ directory? Your external SD should be mounted at /mnt/sdcard, the internal sd card at /mnt/sdcard2. Is it possible that your SD is partitioned (e.g from clockwork mod)? I think that backing up, formatting your SD and restoring the data might be your best bet.
This sounds a lot like you might have some sort of problem with your SD card or permissions on your SD card. In fact, do you even have an SD card in the phone? The script relies on that to backup your old dictionary.
This isn't something I can particularly help you with! Try running 'Fix permissions' in clockwork recovery then try again, although this won't necessarily fix permissions on the SD card. As far as I'm aware, the easiest way to fix SD card permissions is to format the card and then copy all your data back. That the file manager is failing to read the files from your SD card has nothing to do with the files themselves, I shouldn't think.
So what do I do if I'm writing British English most of the time, but I also want to write texts in French, Spanish and Portuguese... :S I never knew that SMS message settings were specific to countries!
I believe you're meant to flash that zip through clockwork mod. Just for the record, no renaming of files is necessary, all the apks are recognized by the system, but if you keep the original file it shows up as a non-working duplicate (in Settings -> Spelling Correction you will have two 'Android' options).
I also used ES File Explorer to do this the first time, and it worked fine. Bear in mind that you have to go to Settings -> Spelling Correction, press the settings button, and select the correct dictionary.
Strange, I'll look at this tomorrow. The mac script definitely works, and most of the work (moving the files into the right place and changing permissions) is done actually on the phone, so the only problem I can think of is that the windows .bat isn't pushing the files on to the phone in the first place. I'll check the .bat file on a PC at work tomorrow and see what the crack is. It's probably got the wrong line breaks or something.
That's odd, my Android keyboard is still there - My Huawei IME didn't have predictive until I specifically turned it on in settings. Can you check that LatinImeGoogle.apk and LatinImeDictionaryPack.apk exist in /system/app?