I was searching for this exact same request but it looks like this went unresolved, so I hope this helps.
For in-page translation there is the following workaround:
- Install the Google Translate extension.
- When you're on any page in Opera, hit CTRL-ALT-P or right click and select Google Translate>Translate page to [language].
Your page will be translated, not as intuitive as Google Chrome's in-page auto translation, but just remember the keyboard shortcut or right click and you get close to the same result.
There have been recent RAM issues with Chrome (5GBs of ram for 20 tabs?!) I also tried Firefox, which seemed to solve the RAM issue, but it did use a lot of CPU resources, which I didn't feel was normal, Opera however doesn't seem to have either of these issues.
I can have Opera running with 30+ tabs without experiencing RAM or CPU issues - This is why i like Opera over any other browser - on Windows 10...