A quick update.
I just realized this happens on YouTube for me, as well. If I watch a string of K-pop songs with translations to various languages, normally it shows English for me, as I chose it. However, now it will chooses the default language of the video (mostly Korean). After refreshing the page it immediately “forgot” that I clicked I wanted English lyrics. My conclusion is that cookies are not working.
I checked if the problem with Viki is persistent on other browsers asides from Chrome which I usually use. And it is, Opera and Safari show the same problem.
Interestingly, getting English on YouTube videos is no problem if you log out, since English is the default language on YT.
Meaning, personalized cookies (the ones after you log in into YouTube or Viki) are not being used and updated. On any browser.