Unfortunately it looks like the log action text is stored in the db as a plaintext and in the content language. Special:CheckUser behaves the same way. It also seems not feasible to store it in the user language, because at the time of storage that would be the language of the target not the checkuser. The way it's stored probably has to be changed to make this possible.

In T268379#6639375, @Ammarpad wrote:

Unfortunately it looks like the log action text is stored in the db as a plaintext and in the content language. Special:CheckUser behaves the same way. It also seems not feasible to store it in the user language, because at the time of storage that would be the language of the target not the checkuser. The way it's stored probably has to be changed to make this possible.

You are right. I just tested with the "old" checkuser tool and indeed log entries never get translated, which is a problem for crosswiki volunteers such as stewards when performing checks on other projects, not being able to read/understand some of the information returned by the tool.

Do we have a task to change the way info is stored? Or maybe repurpose this task to that goal.

Oh, my memory... I just found T41013: Incomplete i18n for log entries in CheckUser created by me in 2012...