Not a long ago, Google removed Opera/Presto support and blocked proper functioning of their web sites in Opera 12. But if you set a proper masking you can get the most of Google's resources working in Opera 12 again!

Use this instruction: https://forums.opera.com/topic/5577/new-youtube-problems-with-opera-12-17/32
Also, add the user-agent masking for "google.com" by editing override.ini and using this custom User-Agent string: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:32.0) Gecko/20100101 Firefox/32.0 Opera 12.16

And you'll get:

Working Youtube's comments (displaying and commenting)
Working Plus.google.com portal
Valid google search engine (instead of simplified half-functional design) with the most of functions working (such as "find similar image") again.

Thanks, that fixed YT at least, but it broke paypal. I guess i will finally have to move out of opera.

Im not only seeing this issue with youtube. It has happened on other sites aswell. But the errors do not appear in other browswers, or even in Opera 24

Thanks for the tip but that's not it.

Im having some strange text related issues with opera 12.* All text seems to overlap and is unreadable, but only on some webpages. Picture link from youtube comments here http://imgur.com/1irCqiL

As you can see it's not pretty. I have tried uninstalling and deleting the ..\roaming\Opera\ folder. No luck. It's driving my crazy, and i bet it's just a simple issue or something i have overlooked.