opt-in text needs translations

[andrewcmyers]

The page https://civs1.civs.us/cgi-bin/opt_in.pl exists in an English version, but it's a page seen by a lot of users whose first language is not English. So it would be good to add translations for the several languages that CIVS supports.

[andrewcmyers]

French and German are the most commonly used languages other than English, so those are the top priority. But of course I'd like to cover all the supported languages.

[andrewcmyers]

French, German, Russian, Chinese, Spanish are now covered.

[andrewcmyers]

There is now machinery for translating the pop-up messages as well, although currently only English is supported.

[andrewcmyers]

good enough for now.