Are checklists always written in English? Are checklists normally written in English? If pilots are native speakers in another language, is it possible/legal for them to use the translated version of the checklist?

This may be different for the small private aircraft and commercial airliner. Please cover multiple cases when possible.

Soviet Union pilots probably used Russian for checklist. However I ask about open, developed countries (Germany, France, etc) and planes that are used all over the world.
It is definitely common here in Germany to use German checklists (German is not an ICAO language).
see http://www.motorflugschule-egelsbach.de/Downloads/Diverses/C172_R04.pdf for example. 

However since many systems and acronyms used have English terms anyways it boils down to a combination with English.