I'm using two languages for my site "en" and "ru". My Gengo settings are
Gengo should append language codes to permalinks automatically - TRUE
Allow visitors to read this site in a combination of languages - FALSE
Let Gengo choose the best languages to display - TRUE
Set blog default language: Russian
I have been writing RU posts into my blog without Gengo installed during last year. So there are a lot of links in Google without "/en/" or "/ru/" postifixes in urls.
So I found a problem, if user hasn't set gengo cookies in browser and opens old links from Google for a first time he gets Redirect Loop. But if user has opened blog's index page and try to open url without "/en/" or "/ru/" at the end all works fine.