Just to further clarify, your chances of any type of free upgrade to Delta One or KLM World Business Class on an international flight are extremely low as a gold. If they have oversold coach, they may give a few free upgrades to make room for everyone, but those will almost always go to the highest level elites (Diamond and maybe Platinum) flying on the most expensive coach tickets. They will prefer to let these fly empty rather than upgrading someone for free.

The unlimited free medallion upgrade program is only available on flights within North America.