Lergo-166 : if a question is added to a lesson, that the fields
subject/language are not defined...
Lergo-236 : site language for Russian should be: Русский (i.e. the first
letter is capital letter).
Lergo-223 : unregistered user tries to click on "create" or use "invite
student" to lesson feature
Lergo:227 : added tip
Merge pull request #100 from lergo/lergo-223

Lergo-166 : if a question is added to a lesson, that the fields