Where is the library for icu-i18n ?

[bob prohaska]

In playing with compiling firefox on raspberry pi the process has gotten
far enough to report:

DEBUG: configure: error: Library requirements (icu-i18n >= 58.1) not met; consider adjusting the PKG_CONFIG_PATH environment variable if your libraries are in a nonstandard prefix so pkg-config can find them.

What's the best fix or workaround? I can't find a library or sources that
seem to come close to satisfying the requirement. The system is -current,
the ports tree was updated  on 3/21/2017.

Thanks for reading,

bob prohaska