brew cask install dia
After his it won't run because DISPLAY=:0 env var is not set
vim /Applications/Dia.app/Contents/Resources/bin/dia
Add the following content to line 40 (right before the oascript call)
#########################################################
# Ref: http://navkirats.blogspot.de/2014/10/dia-diagram-mac-osx-yosemite-fix-i-use.html
versionOSX=$(sw_vers -productVersion | awk -F '.' '{print $(NF-1)}')
[[ ${versionOSX} -ge 10 ]] && export DISPLAY=:0
#########################################################
Worked for me! Thanks!