For adding tags to a course, forum, etc., an autocomplete form is used that interprets the comma as a separator. Pressing the comma key is handled the same way as pressing enter, the semicolon is used as a normal character. My suggestion is to use both comma and semicolon as separators. This can easily be achieved, just the if-statement in lib/amd/src/form-autocomplete.js, line 686 (v3.5.17), has to be modified. Replace

if (e.keyCode === KEYS.COMMA) {

with

if (e.keyCode === KEYS.COMMA || e.keyCode === 59) {

 That's all.