I've found that it could possibly mean "I'm sorry (for)" but I just want to. Source is below:
http://www.daltai.com/discus/messages/1 ... ?947046629

Is the word "for" included in the sentence so as a result, the whole phrase translates to "I'm sorry for..." e.g. I am sorry for your trouble = is dona liom do bhris.

Secondly, I want to confirm the translation of "Is bocht liom". I've found it could also mean "I'm sorry".
If this is the case, is there a difference between "Is dona liom" and "Is bocht liom"?

I think those would be dialectical differences.

In Conamara we say to grieving people: Ní maith liom do thrioblóid. Sorry for your loss. (I don't like your trouble)
And the reply is: Tá's 'am sin. - I know that.