Possibly a typo, but the far right router is shown with a WAN address of 192.168.88.30, should be 192.168.3.<something>
Ensure NAT is turned off on all routers.
Are you using a routing protocol (RIP, OSPF, ??)
Can you ping the Internet (188.8.131.52 works) from each router along the path?
Can you ping the workstation, or at least the 192.168.4.1 interface, from each router?
Do routes exist in each router to the .4 subnet ? Default routes will find the path out, but not back. All 4 subnets (192.168.1.x, 192.168.88.x, 192.168.3.x, and 192.168.4.x) should appear with valid next hops in each router.