Most other errors also boil down to Cocoa specific APIs being used ion Java, such as GCD, specific string APIs, arc4random() (which is a C level Posix API), etc.
Remember that Silver is the Swift language, for different platforms. You are still targeting the Java platform and its APIs. Silver does not port Cocoa and the iOS/macOS SDKs to other platforms.
i did lng one issue for [weak self] throwing the compiler off:
78119: Swift Compatibility: [weak self] syntax for blocks does not compile