musicpd automatically detects if Avahi has already been installed and if so, links to it. However, Avahi depends on intltools, but the *.pc files for Avahi don't note this, so when musicpd attempts to build against it, it fails because it can't find the required symbols.

cc -O2 -fno-strict-aliasing -pipe -I/usr/local/include -o mpd mpd-audioOutput_alsa.o mpd-audioOutput_ao.o mpd-audioOutput_oss.o mpd-audioOutput_osx.o mpd-audioOutput_pulse.o mpd-audioOutput_mvp.o mpd-audioOutput_shout.o mpd-audioOutput_jack.o mpd-_flac_common.o mpd-_ogg_common.o mpd-oggflac_plugin.o mpd-oggvorbis_plugin.o mpd-aac_plugin.o mpd-audiofile_plugin.o mpd-flac_plugin.o mpd-mod_plugin.o mpd-mp3_plugin.o mpd-mp4_plugin.o mpd-mpc_plugin.o mpd-audio.o mpd-audioOutput.o mpd-buffer2array.o mpd-charConv.o mpd-command.o mpd-conf.o mpd-dbUtils.o mpd-decode.o mpd-directory.o mpd-inputPlugin.o mpd-inputStream.o mpd-inputStream_file.o mpd-inputStream_http.o mpd-interface.o mpd-list.o mpd-listen.o mpd-log.o mpd-ls.o mpd-main.o mpd-metadataChunk.o mpd-myfprintf.o mpd-normalize.o mpd-compress.o mpd-outputBuffer.o mpd-path.o mpd-pcm_utils.o mpd-permission.o mpd-player.o mpd-playerData.o mpd-playlist.o mpd-replayGain.o mpd-sig_handlers.o mpd-signal_check.o mpd-sllist.o mpd-song.o mp
 d-state_file.o mpd-stats.o mpd-tag.o mpd-tagTracker.o mpd-tree.o mpd-utils.o mpd-volume.o mpd-utf8.o mpd-zeroconf.o mpd-locate.o mpd-storedPlaylist.o -pthread  -L/usr/local/lib /usr/local/lib/libiconv.so -lid3tag -lz /usr/local/lib/libmad.so /usr/local/lib/libfaad.so /usr/local/lib/libvorbisfile.so /usr/local/lib/libvorbis.so /usr/local/lib/libOggFLAC.so /usr/local/lib/libogg.so /usr/local/lib/libFLAC.so /usr/local/lib/libaudiofile.so -lm /usr/local/lib/libavahi-client.so /usr/local/lib/libdbus-1.so /usr/local/lib/libavahi-common.so -pthread mp4ff/.libs/libmp4ff.a -Wl,--rpath -Wl,/usr/local/lib -Wl,--rpath -Wl,/usr/local/lib
/usr/local/lib/libavahi-common.so: undefined reference to `libintl_bindtextdomain'
/usr/local/lib/libavahi-common.so: undefined reference to `libintl_dgettext'
/usr/local/lib/libavahi-common.so: undefined reference to `libintl_bind_textdomain_codeset'
*** Error code 1

Stop in /usr/ports/audio/musicpd/work/mpd-0.13.0/src.
*** Error code 1

Fix: Patch attached with submission follows:
How-To-Repeat: portinstall avahi-app
portinstall musicpd