The font textures from german "Umlaute" (äÄöÖüÜß...) and maybe also other characters are not loadings from resource packs (I tested the same font textures in older Minecraft Versions (1.8.9). there its working correctly). Its not working since at least Minecraft 1.15. I also testet at least 5 different Ressource Packs with custom fonts. Non of those are working (The "Umlaute") but the letters are in the Texture Pack Font File.
MC-216946
German Special Letters / Umlaute (äÄöÖüÜß...) are not loading from Resource Packs
Resolved
Invalid
0
This is an issue with your resource pack. It's definitely possible to retexture these characters in 1.15 or above, but it works differently than in previous versions.