To answer your question specifically, I'm used to "English (intl, with AltGr dead keys)" but in Linux Mint there are like 20 options. I was trying "US, intl, AltGr Unicode combining" or perhaps "US, intl, with dead keys" or such. (I've tried about a dozen in the last 2 days.) Instead of an apostrophe, they were generating what could become an accent mark, a stress mark or diacritic depending on the next letter. On "with AltGr dead keys" you must use right alt+apostrophe for that effect. (The quotation marks would do the same thing.)
Anyway, the keyboard lets me type things like þðßáœßðfhëü´6´^¨¼²³¤` with 2 buttons like shift to make a capital! This is good for German, Spanish and French, but Hungarian and Romanian require 3 buttons, then a 4th which is more tedious.
left alt shift 5 = ş ţ romanian
left alt shift 3 = ā lines for latin
left alt shift 2 = ű ő - hungarian long umlaut
On some keyboard layouts, pressing the quote mark starts a modifyer and then depending on the layout the following character is combined with the quote mark. Most English layouts don't include ś in this, but some Eastern European (?) languages use that character more often and so include them in this modifyer shortcut.
