How many should be kept, if not just the last as for comments? (You sound like you want/need more than that.)

Would they appear inside the text of the entry (in which case there's no limit to how many are kept, other than the entry size limit) or as metadata, like they are for comments? (The "edited on" and "reason for edit" field labels are only translatable if the history is stored as metadata, so the "inside entry text" option also has downsides.)