> 1. What's the default transaction isolation level?

For Jaybird - TRANSACTION_READ_COMMITTED.

> 2. How do I translate Firebird terms SNAPSHOT WAIT into JDBC terms? Is there
> a translation matrix somewhere?

yes, there is file isc_tpb_mapping.properties in the driver.

> Does your example above set transaction
> isolation level to SNAPSHOT WAIT?

No, to READ COMMITTED NO WAIT.

SNAPSHOT WAIT in Firebird uses isc_tpb_concurrency + isc_tpb_write +
isc_tpb_wait, you can map this to any JDBC isolation level, however in
order to keep the semantics close to what is written in JDBC specs, map
it to either TRANSACTION_REPEATABLE_READ or TRANSACTION_SERIALIZABLE.

Roman