Translation:That must be discussed with Dewi Lingo.
Hmm. There is no mention of 'you', 'we' or whatever here, so I would be inclined to treat it as a shortened form of:
mae rhaid trafod hwnna gyda DL (literally - 'there is a need/want of discussing that with DL') and to translate it as:
'that needs to be discussed with DL' or similar.