How often do publications get translated into other languages?
In my field, articles are rarely translated. At best, an articles abstract might be in 2 or even 3 languages depending on the journal. For whatever reason, English is the de facto language of the majority of research.

For books it's a little different. If the book was highly influential it will be translated into other languages. However, it takes often several decades for a book to reach the level of prominence that it is translated into other languages. Again this is because a lot of highly influential books are originally written in English. 

The process of translation (for books as articles are rarely translated in my field) depends. Sometimes one person who is fluent in both languages will translate the book for scholarly output. At other times a team will work together to develop the translated edition.