I spent a very enjoyable 2 weeks in Taiwan a couple of years ago.
English is widely spoken and understood although sometimes with difficulty. Public signage is mostly in both chinese and english, including bus destination signs.
I am unsure about train fares, but for memory they are fixed and do not vary as in UK.
On the high speed line between Taipei & Kaoshiung reservations are advisable at busy times. The service is time interval with hourly expresses and hourly stopping services spaced at the half hour. 3 cars at the Taipei end are always unreserved. For important journeys I recommend booking online.
On the ordinary lines, reservations are advisable on other than local services. The longer distance trains tend to be packed with standing room at times so dense you cannot see out of the windows across the carriage.
The ticket machines are in both chinese and english. I had no problems and only encountered a chinese only situation once.
When you arrive in Taipei go to the main station and at the enquiry window ask for an english timetable. These are pocket size folded documents and list all but the local services.
For the Taipei metro you can buy a day ticket at any station enquiry office. There is a refundable deposit. These are RFD cards like Oyster. They work very well. For single journeys a RFD token will be issued from the ticket machines. Kaoshiung metro is the same. The tickets are NOT interchangeable between the 2 cities.
It always helps to have a Taiwanese friend, of any gender, to assist with language although it is doubtful that you will have problems.
In Kaoshiung there is a small rail museum with several locomotives and an interesting display.
It is worth visiting some of the mountain railways. These can mostly be done with day trips from Taipei, the mountain trains leaving from a junction station on the main line. A day trip to Hualien is well worthwhile, but get reservations at the ticket office.
