Birthdays in Germany are sacred and therefore should never be acknowledged BEFORE the actual date of the birthday. Any early birthday “Congratulations” would be considered bad luck. There have been times I have been frustrated by not understanding how family and friends couldn’t/wouldn’t say Happy early Birthday knowing that they weren’t going to see that person again until after their birthday. Instead a week, two weeks AFTER the birthday, its perfectly acceptable to say it. For any American, we would be perfectly fine saying Happy Birthday before or after.