i just upgraded to 2.6.1 using the automatic updater and it caused a redirect loop on my site. whenever i would visit it it would be like "the address /en/en/en/en/en/en/en etc was in a repeat loop that would never be resolved"
i pulled my hair out for a minute but then figured it out. just go to the permalinks settings page (in wp, not gengo) and hit save. no change, just save. that fixed the problem!