This is a hard one to answer.
I would first have a couple of questions:
1. Was this handwriting or printing?
2. Was it definitely a different language? (my comments are assuming it is English, just very sloppy)
3. Does the tech have an underlying medical condition that prevents him from keeping his hand steady during certain tasks?
I disagree with your statement about his schooling. You would have no way of knowing how hard he tried in school. I have been involved in Auto shops for over 25 years and I've seen handwriting and printing of all degrees of neatness and from people both young and old. I personally have to print everything. It's still not the neatest but is is readable. If I used my handwriting, a pharmacist couldn't decipher it. But as an employee I would probably not offer up my reason for sloppy handwriting...which just so happens to be a nervous system issue. I take pride in the work I do.....I'm concerned with quality no speed. So the handwriting may have no bearing on the work.
I think you should take the time to coach the employee, on proper techniques for how you want the repair orders filled out. If that means he prints instead of writes, than so be it.
If he wrote it in a different language, than you have the write to reuire him to be able to read and write in English.