Set enviroment variables

export ICU4X_BUILD_MODE=checkout
export LOCAL_ICU4X_CHECKOUT=/path/to/icu4x/repo

To run the app in JIT mode

dart --enable-experiment=native-assets run

To run the app in AOT mode

dart --enable-experiment=native-assets build bin/dart_intl4x_example.dart 

which builds the executable in bin/dart_intl4x_example/.