Java fails to start on Windows 10 with non-ASCII characters in the path if current regional format differs from the system locale.
(Settings | Time & Language | Language | Administrative language settings | Administrative tab | Language for non-Unicode programs | System locale: X)
(Settings | Time & Language | Regional format | Current format: Y)

For example, jdk15 fails if java path contains German characters and:

System locale: German (Germany)
Current format: English (Europe)
Region: Germany
Active code page: 850

> C:\qwertz-ßüöä\openjdk-15-ea+17_windows-x64\bin\java -version
Error occurred during initialization of VM
Failed setting boot class path.

Previous jdk versions work ok in this case:

> C:\qwertz-ßüöä\openjdk-11+28_windows-x64\bin\java -version
openjdk version "11" 2018-09-25
OpenJDK Runtime Environment 18.9 (build 11+28)
OpenJDK 64-Bit Server VM 18.9 (build 11+28, mixed mode)

> C:\qwertz-ßüöä\openjdk-13+33_windows-x64\bin\java -version
openjdk version "13" 2019-09-17
OpenJDK Runtime Environment (build 13+33)
OpenJDK 64-Bit Server VM (build 13+33, mixed mode, sharing)

> C:\qwertz-ßüöä\openjdk-14+36_windows-x64\bin\java -version
openjdk version "14" 2020-03-17
OpenJDK Runtime Environment (build 14+36-1461)
OpenJDK 64-Bit Server VM (build 14+36-1461, mixed mode, sharing)

Jdk15 and jdk14 fail if java path contains Russian characters and:

System locale: Russian (Russia)
Current format: English (Europe)
Region: Russia
Active code page: 866

> C:\йцукен\openjdk-15-ea+17_windows-x64\bin\java -version
Error occurred during initialization of VM
Failed setting boot class path.

> C:\йцукен\openjdk-14+36_windows-x64\bin\java -version
Error occurred during initialization of VM
Failed setting boot class path.

Old jdk13 and jdk11 versions work ok:

> C:\йцукен\openjdk-11+28_windows-x64\bin\java -version
openjdk version "11" 2018-09-25
OpenJDK Runtime Environment 18.9 (build 11+28)
OpenJDK 64-Bit Server VM 18.9 (build 11+28, mixed mode)

> C:\йцукен\openjdk-13+33_windows-x64\bin\java -version
openjdk version "13" 2019-09-17
OpenJDK Runtime Environment (build 13+33)
OpenJDK 64-Bit Server VM (build 13+33, mixed mode, sharing)