On MacOS, I configured PG10 beta2 sources with '--with-icu" option along with ICU_LIBS and ICU_CFLAGS env variables to define the location of the ICU libs that I built. Once the staging is ready, I executed initdb but it fails with the following error:
$./initdb -D /tmp/data
The files belonging to this database system will be owned by user "buildfarm".
This user must also own the server process.
The database cluster will be initialized with locale "en_US.UTF-8".
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".
Data page checksums are disabled.
creating directory /tmp/data ... ok
creating subdirectories ... ok
selecting default max_connections ... 100
selecting default shared_buffers ... 128MB
selecting dynamic shared memory implementation ... posix
creating configuration files ... ok
running bootstrap script ... ok
performing post-bootstrap initialization ... 2017-07-12 11:18:21.187 BST [53618] FATAL: could not open collator for locale "und": U_FILE_ACCESS_ERROR
2017-07-12 11:18:21.187 BST [53618] STATEMENT: SELECT pg_import_system_collations('pg_catalog');
child process exited with exit code 1
initdb: removing data directory "/tmp/data"