Java approach: create the JVM to support one language, so it has rich high-level concepts that are unfortunately skewed toward certain assumptions about language design, and it can be reused only for other languages that are similar enough.

WASM approach: start very low-level so C is definitely supported. Thus everything is supported, although every language has to roll its own high-level constructs. But over time more patterns can be standardised so languages can be interoperable within a polyglot WASM app.