I've been working on some Word documents, some of them mine which have had a busy life, passing from memory sticks and other computers, some recently downloaded from the internet.

When I go to edit some of them, deleting the text (in English)and type the replacement it's in Thai script.

I've played with the tools/language settings to no avail. I fixed a couple by copying them and emailing them to myself which changed the format to an editable form.

Then today an old document of mine wouldn't fix itself by this method and finally I had to copy it off another website where it was published several years back and paste into a new document, where it edited ok.

Funny how MS Word is a bit of a blind spot for most computer geeks, I know a few of it's foibles myself through sheer weight of usage but it's only a drop in the bucket.

I don't have a Thai script program installed that I know about.

I've looked into MS 2003 Office tools and Thai has apparently been permanently enabled when I had the laptop fixed in Chiang Rai this year.

Every other language can be disabled but not Thai.

Not sure I understand your problem clearly, but ............

Have you tried pressing and holding [for one second]

the key to the left of the "1" key ?

That toggles the keyboard from Thai to Eng and back again.