Changing Keyboard/Input Source order on MacOS
It is impossible to re-order them. To fix it, you want to tick Show Input in menu bar. This will cause a little icon to appear in your menu bar with your language:



(The icon might  be different depending on the language set). If you click there you can change the language to U.S. International - PC. 

If you still want to use another language for a specific app (say you want to use English for all apps except Safari where you want to use Russian), you can either:


Change the language in the menu bar
Keep Automatically switch to a document's input source checked which will remember your last language for that application