There is something funny i noticed at the end of october after my upgrade to Ubuntu 18.10 (yes, i know: this thread is for Mint, but Mint is based on Ubuntu, so FWIW):
i tried to update to Lazarus1.8.4-dfsg (or whatever the cryptic thing is) via Synaptic from official repo.
it failed.
I removed everything having to do with fpc/lazarus
Installed from Synaptic/Ubuntu-Repo. Worked!
Now the weird part: When i was reconfiguring the Lazarus-IDE to my taste, the recompiling of the IDE failed --> Units missing!!!
WTF?!?!?!?
Since i have a working Laz1.8.4-Installation on a Windows-PC, i searched the Folder-Tree on the Win-PC for those Units, and color me surprised: they were there.
OK, Synaptic --> Remove FPC/Lazarus
Download the deb's from here
install using sudo dpkg -i
Everything fine, no missing units, IDE recompiles etc.
NOW: What i found out (and to clarify: i'm in no way a Linux-expert):
The install from Synaptic/official Ubuntu-Repo uses different install-paths than installed via deb?!?!?!