We have the same problem. As we develop an app (with Flutter) for German users that can not read, it is critical to us. The older German sound packages are working fast, but sound very bad. Any other language package that we tried (en, it, fr) works fine / fast.
3 seconds delay:
{locale: de-DE, name: Anna}
{locale: de-DE, name: Martin}
{locale: de-DE, name: Helena}
fast (but old):
{locale: de-DE, name: Sandy}
{locale: de-DE, name: Shelley}
{locale: de-DE, name: Grandma}
{locale: de-DE, name: Grandpa}
{locale: de-DE, name: Eddy}
{locale: de-DE, name: Reed}
{locale: de-DE, name: Rocko}
{locale: de-DE, name: Flo}