For Opera, or any application that may be buried in an unknown location, there are several ways to locate the application files, including spotlight searches and some terminal commands; however, in the case of applications that will open with contextual menu shortcuts, the simplest way to do this is the following:
Launch the Opera browser (or other application) using the 'open with' submenu in the contextual menus. The browser should display in the Dock as a normal application would.
Right-click the application and select the "Show in Finder" menu item. This will open a folder containing the browser.
Remove the application by deleting it.
Repeat this as long as the application can be located in the Finder in this way (users may have to restart their computers after each deletion to update contextual menus and other application links).
Here's a detailed tutorial about how to do clean and complete uninstall of Opera Mac.
Have you tried going into System Preferences > Language & Region > Region to check whether it's set there to China?
As for your bookmarks, I don't know where they are stored; there isn't a .plist or a library container which gives them and if they're in the application package, I can't find them there either. One of the devs on the Mac side will have to answer that question, and it might depend on which version of the OS you had when you made those bakups.
I'm using the latest public release of Opera on MacOS 10.14.2.
Safari and Firefox don't even use the same Flash as Opera. And, like I said, it seems more of Chromium or site issue.
And by the way, it seem to have worked only on IE here. Maybe because there is no Flash for Opera installed.
@leocg I think I may have resolved my own problem and the result seems embarrassingly obvious. The stop loading icon is hidden under the reload icon on the left next to the forward and backward icons in the navigation buttons area. When a search is being performed and a page is loading or being reloaded the Reload icon will change to an X and can be clicked on to stop the process. I do feel a little silly but I always felt there was no such thing as a bad question, at least most of the time.