Have you just added numbers like I, IV and so on or did you enter I., IV., XI. and so on? In first case it will not work, the abbreviations in the list must be followed by a dot. And of course you have to recreate the sdlxliff file after adding the abbreviations to the list, as an already segmented file will not be resegmented just by amending the list.

Of course, these abbreviations followed by a dot were added before preparing the SDLXLIFF file:

Sandor Juhasz

I guess another way to tackle this would be to use exceptions to the full stop rule.  So I can achieve this with three rules from a default TM:

Might be better ways but just tested quickly with these:

But... I can also use the abbreviation list just by adding these:

XII.

X.

V.

So I'm not sure why this doesn't work for you.  It sounds as though you are either not using the TM you think you are, or you have some other overriding rules in there getting in the way.  Maybe test with a default TM and add the abbreviations just to see if it works for you or not?

I tested it with a default TM. It really works.

I have a lot of abbreviations added to my existing TM. Can I export them to a new default TM or should I add them one by one?

I tested it with a default TM. It really works.

I have a lot of abbreviations added to my existing TM. Can I export them to a new default TM or should I add them one by one?