As reported by a Spanish language user in a forum post, some columns in some Moodle reports are allways shown in the English language, and can not be translated. I believe them to be the names of Moodle function calls (but I am not a programmer).
I just added some text and screengrabs about this in the Developer documentation, but maybe these non-translatable texts show up in other places in an otherwise fully translated Moodle site.
I will really appreciate if anybody else can comment whether he/she has seen/heard this issue in a fully translated non-English site.
