Fix Solutions i18n issues

@chrisndodge @muhhshoaib @martynjames : this fixes some i18n problems introduced in 
https://github.com/edx/edx-platform/commit/2cc0433833bee4ccfb4955bfdbbff0edc363920a

We need to be really careful with i18n, it causes me a lot of headache when stuff is improperly marked up for i18n, because I have to drop everything, deal with translators, and make PRs to fix strings. Please read through https://github.com/edx/edx-platform/blob/master/docs/en_us/developers/source/i18n.rst and ask me if you have any questions.
Hi @rlucioni pinging @griffresch from Product on this, but I'll answer as best I can.

This email is sent to a user who has purchased multiple seats in a course. This area of the email is a suggested template (not Mako template) that this user should use when forwarding on the Registration Codes to the students that wish to redeem them.

Sample use-case:

GE wants to buys 100 seats to a course. Jane - the person responsible for these 100 seats - goes through the purchase flow and set the Quantity to 100. Jane receives this email from edX with a list of 100 Registration Codes. Jane then uses this suggested template, to give instructions to her 100 users that wish to enter the course.

So back to your original question. IMO, this seems translation-worthy, although I could see that it'd be hard to give enough context to translators.