This is something that we have talked a lot about internally and have also heard a lot of requests for from Network Creators. It's tough because Ning Networks are so diverse in their level of customizations (many networks use their Language Editors heavily) and also in how their members interact (a lot of posts may contain slang or other familial language not always easily translated).
One option we've considered is to allow members to change their translations for all Ning-generated text and leave any content untranslated. This is definitely not off the table and is something we'd still consider for future implementation, but we don't have anything scheduled for it yet.
I personally think that this option you are considering would be the perfect solution.
Not sure if this helps, but the JenBar has a built in Google translation and I've set mine to Turkish for the sake of this demonstration. I have no idea how accurate the translation is since I do not speak Turkish, but have a look. It just might be a quick solution for those needing it.
Scroll to the bottom to see the JenBar (available through Jen Social VIP) in it's full glory. I have the language translator set to Turkish.....I did have to use an Ad Box for this, but I love it!
I have had installed several types of bars to try them, but although they are a good alternative usually put the slower networks.
But lways remain an option.