Thank you both for your replies. From the clues here and some looking around, I was able to find the offending parts of both doctext.inc and rep111.php and replaced "VAT no." with "Tax no." and all appears to be working. I did it on each of the various forms and reports. I guess there is no way to know if we'll run into trouble until we use the programs more, but I marked down the filenames and lines of code I modified so they can be put back if needed.
I'm still wondering if a part of my FA instance is missing because "Forms Setup" is not a feature that appears in my Setup window.
Regarding the length of the comments field, it sounds like a winning strategy to force a new line character after so many characters. I am not a PHP coder so I wouldn't even begin to know how to do this. Any suggestions?
Thanks