Fix a decode error in course_about.html and make some string translatable

The strings in share links should be in unicode, otherwise when the name of a course is non-ascii, it will generate a decode error.
And some of these strings is actually translatable, so they should be collected into mako.po.
Merge pull request #3119 from louyihua/translation-fix

Fix a decode error in course_about.html and make some string translatable