A strings isn't localized

[izendegi]

I've seen that there is a string in the header, the one which tells which the grading method is, that isn't localized:

I think that the values there are rubric and marking guide, in that case I believe that these core strings can be used for that localization:
gradingform_guide | pluginname
gradingform_rubric | pluginname

[marcusgreen]

Closing as I have merged in your code. I will mention you in my next changelog update. Many thanks for raising the issue and providing a solution.