If your friend can scan the handwritten Japanese letter, you could put the job out to a freelancer online:
https://www.peopleperhour.com
https://www.fiverr.com

I would favor a native-Japanese speaker for this job, since they're more likely to be up to the challenge of dealing with handwriting and it's not a big deal if the quality of the English output isn't native level - as long as your friend's father can understand it.

(If you were translating marketing copy for publication, you'd either go for a native English speaker or pair your translator up with a great English-language copywriter ... or do neither and produce some hilarious Japlish like many Japanese companies do).