Problem is only with 1,8 (all three versions).   1.12.2 installed fine.

It SAYS that is is successfully installed, but isn't available on the launcher.  It is listed in the versions folder, but the .json file seems too small.

Below is the log the installer produced.  (Something seems to be going wrong at the very beginning.) 

Cleared all caches and browsing data from past 24 hours as a precaution,  Still the  problem.
Also tried recommended and most recent versions.  The same
 

 

Considering library net.minecraftforge:forge:1.8.9-11.15.1.1722: Not Downloading
Considering library io.netty:netty-all:4.0.23.Final: Not Downloading
Considering library net.minecraft:launchwrapper:1.12: Not Downloading
Considering library org.ow2.asm:asm-all:5.0.3: Not Downloading
Considering library jline:jline:2.13: Not Downloading
Considering library com.typesafe.akka:akka-actor_2.11:2.3.3
Considering library com.typesafe:config:1.2.1
Considering library org.scala-lang:scala-actors-migration_2.11:1.1.0
Considering library org.scala-lang:scala-compiler:2.11.1
Considering library org.scala-lang.plugins:scala-continuations-library_2.11:1.0.2
Considering library org.scala-lang.plugins:scala-continuations-plugin_2.11.1:1.0.2
Considering library org.scala-lang:scala-library:2.11.1
Considering library org.scala-lang:scala-parser-combinators_2.11:1.0.1
Considering library org.scala-lang:scala-reflect:2.11.1
Considering library org.scala-lang:scala-swing_2.11:1.0.1
Considering library org.scala-lang:scala-xml_2.11:1.0.2
Considering library lzma:lzma:0.0.1: Not Downloading
Considering library net.sf.jopt-simple:jopt-simple:4.6: Not Downloading
Considering library java3d:vecmath:1.5.2
Considering library net.sf.trove4j:trove4j:3.0.3

Sorry, but Forge 1.8 is not supported on this forum.

We can only help you with the new and supported versions.