Actually, we are not quite clear with your issues so can you please explain it more clearly.
Further, Polylang does work well with the WP Travel plugin. Here we don’t really get what you meant by the “title”and the “currency”. By currency, if you mean symbol then it cannot be translated to any language. What you can do is, you can yourself choose the currecny of your choice from the list for the Trips.
1. When I use the Polylang plugin, I cannot change the currency (like RP.15.000 to $1 or other) when the language has been changed.
2. if you go to the testimonial section on the home page, in the section “WHAT OUR CUSTOMERS ARE SAYING ABOUT US?” I can’t make that change when changing languages. (every title in homepage)
and many other small things.
if I buy a plugin, are all the problems resolved?
If you want the currency symbol be “$” then you can directly chose it from Admin Panel > Trips > Settings > General. There is no any way to convert the RP to dollar using any other plugin and it is not the translation task.
As for the Testimonials section, you can directly add the translated string into the title field from the customizer itself. Since it is input filed you need to directly add the translated string.