A Scot should have no problem understanding the meaning of Auld, coming from a Frenchman.
It needs to be tailored to the nationality of the receiver, however. I don't know what I would tell you to let you know I want an alliance with you... the only Finnish word that springs to mind is Koskenkorva, and that isn't exactly synonymous with alliance. Granted, if I offer you a drink, it means I want to be friendly, but still...
From where comes Finnish? Germanic and Roman languages are usually grouped under the "Indo-European" label, along with other languages, and Finnish is not part of that vast family. Is there a similar "grandfather" for Finnish? I cannot say I have checked those Indo-European roots though: I can only go back as far as Greek.