A small update after some time.
Mainly this update deals with the custom hotkey function.
I've changed the code to use Chrome's Keyboard Shortcuts feature (that link at the bottom right of chrome://extensions). The key press should be more accurate compared to the old method (Wouldn't have noticed if not for Will Lucic's comment).
Speaking of the old method, it uses a content script which was injected into all pages loaded to detect key press. With the switch to the new method this was removed along with the extra permission needed for it. The options page is edited to direct to Chrome's dialog, you may have to scroll down if you have many extensions. The default set is "Alt-Z" ("Alt-X" for SimpleUndoRecents).
Next change is the allowance of "chrome-extension://" URLs.
According to the comment by zloidooraque tab suspending extensions uses these URLs so I edited the regex and allowed them.
Also Serbian and Spanish translations are added, thanks to those who contributed.