I am going to travel between Shinosaka, Kyoto, and Nara in November. I don't speak Japanese and may have trouble communicating with ticketing staffs. Are there vending machine for JR train ticket in those stations? Also, do they accept credit cards (vending machine and/or staff)? Thanks.

You can just tell the attendant what you want to go to x and hold up one finger. You could write the name of your destination in English on a piece of paper.

You could look at the departures board and identify the train that you want and write that down on the paper with the time, destination:
Hikari 333, 14:04 -> Shin Osaka

I think that communicating with the person would be easier than a machine. I don't know about credit cards, think they're ok to use, but would be prepared with cash.

Vending machine is unlikely to work, as I recall instructions are in Japanese only.
One gripe I have about JR system is that they don't take credit card or debit card. They only accept cash and their own C/C. Make sure you have enough cash.

Yes, I visited Kyoto in 2005, and there are plenty of vending machines, and some of them had an English language option as well, so this made it very easy to buy tickets. Just need to pick a machine that has the English option (option was displayed on the home page screen from memory) and follow the instructions given from then on to buy your tickets - I used the JR machine in kyoto to buy tickets to Himeji and Kansai airport and you could also do seat reservation as well on the machines. All of this was very easy because of the English instructions, I tried buying once on the Japanese only machine and gave up as it got too difficult to follow.
I went from Kyoto to Nara on the Kintetsu private line, not JR, and there also was English option on some of the Kintetsu train line machines as well. Haven't been to ShinOsaka but am guessing the same machine set up may be there as well? Sorry don't know about credit card usage in machine but it was easy to use cash.

I agree with mrwnrfl that it is easier to purchase a ticket from the ticket booth rather from a live person than a machine. That said I have used the machines to buy tickets and they are not that hard to understand.

In my experiences the machines and tickets windows CAN NOT process foreign issued credit cards. I tried at Shinjuku and Tokyo stations Tokyo and my cards were not accepted so you must have yen handy.

I have also read about others who have had this experience on various other sites. They do accept Japanese issued visa,mc,jtb, etc. cards though if you have on of those.

Aloha!

should read "I agree with mrwnrfl that it is easier to purchase a ticket from the ticket booth from a live person rather than a machine" sorry too early in the morning here.

I tried to use the ticket machines at Tokyo Station and could not figure them out. I went to the ticket counter and asked the clerk if he spoke English. The answer was "no". Fortunately I had written down what I wanted, showed it to him, and he quickly gave me exactly what I wanted. I paid with a credit card - American Express, I believe.

Another idea is to learn how to say a few useful phrases in Japanese. Or at least how to pronounce words, esp. place names.

If you asked me (in any language) if I spoke Japanese the answer would be no. But if you asked me: "Toire wa doko desu ka" then I would show you where the toilet was.

if you can't read the signs on the ticket machine, just buy the lowest price ticket from the machine. When you get to the ticket gate at your destination, the gates will swing shut & you will be told to pay 'fare adjustment fee'. Look for the 'fare adjustment' machine which will be near the gate, insert your ticket, pay the amount it says then go through the ticket gate again & you should be good to go!