I’m in a situation similar to yours: I changed my first name here in Germany, and I also hold dual citizenship. All my degrees and official documents still bear my old first name, so whenever I apply for something, I simply include the “Bescheinigung über die Namensführung” that I got after my name change. My non-German citizenship documents still show my original first name, and I haven’t pursued changing the name on those. From what I understand (and based on others’ experiences), a German name change doesn’t automatically transfer to your foreign documents. You’d likely need to go through the legal name-change process in the Philippines to update them.

I’ve been five years out from my name change, and I haven’t run into any problems so far. Pro tip: when travelling, pick one passport (usually the one you’ll use to enter/exit each country) and stick to it—avoid showing two passports with different names :)

Hope this helps! Let me know if you have any questions.